The world of Game of Thrones is so vast that it can be difficult for casual viewers to keep all of the locations, characters, and religions straight. Although it wasn’t featured last season, Harrenhal is still a major location that’s important for viewers to remember going into season seven.

Viewers of the show most likely know Harrenhal as the Lannister army base in season two. The huge, ruinous castle was the backdrop for Jaqen H’ghar as he delivered on his promise to Arya to take three lives for her. It’s also where Arya served incognito as Tywin Lannister’s cupbearer, and the setting for Brienne versus the bear in season three.

However, there’s a lot of history behind the castle that you probably missed if you only watch the show and have never tackled George R.R. Martin’s A Song of Ice and Fire series. It was an important location during Robert’s Rebellion, and it might even hold a significant role in these last two seasons if some fan theories are correct. Curious? Here are 15 Things You Didn’t Know About Harrenhal.

Beware -- this article is dark and full of spoilers.

15. It’s the largest castle in the Seven Kingdoms

A character looking at the ruins of Harrenhal in Game of Thrones.

You might be surprised to learn that the Red Keep, the castle in King’s Landing, isn’t actually the largest castle on the continent. Although the Red Keep is the home of the Iron Throne, Harrenhal is both older and larger.

Construction of Harrenhal started decades before the Targaryens united Westeros under one crown. House Hoare, the rulers of the Iron Islands, decided that the rainy islands actually kind of sucked. (If only the Gryejoys were so wise.) King Harwyn Hoare ventured out and conquered the Trident and the Riverlands, the ancestral land of Catelyn Stark. Years later, one of his descendants would order the construction of Harrenhal. Since it was to be a monument to himself, he wanted the castle to dwarf every other structure in Westeros. Centuries later, his record still hasn’t been beaten.

The kitchens alone are as large as Winterfell’s great hall. Harrenhal’s great hall, meanwhile, was dubbed the Hall of the Hundred Hearths for its size -- even though it only has thirty-five hearths tops, it’s still big enough to entertain an entire army. The whole thing is better suited for giants than humans.

14. It lies to the north of the largest lake in Westeros

Fittingly, the largest castle on the continent also lies at the tip of the largest lake. The Gods Eye is named for its size -- when Arya sees it in A Clash of Kings, she realizes that she can’t even see a far shore. Think of it as a Great Lake in the middle of Westeros.

The lake itself also has a lot of history to it. In the middle of the lake is the Isle of Faces, where the Children of the Forest formed a pact with the First Men to end their war. The island is sacred and has one of the few godswoods in the south of Westeros. As the seasons change in Westeros (and as the violence grows even worse), the color of the water becomes grim. In the summertime, the waters are a beautiful blue and green that glimmer in the sunlight. During winter, however, the water looks more like steel.

13. It was named for its founder, Harren Hoare

Harren Hoare from Game of Thrones

To be sure that no one could forget which person ordered the construction of the monstrous Harrenhal, the castle is named for its founder -- King Harren Hoare, also known as Harren the Black or Black Harren. Harren Hoare was the last King of the Iron Islands, partially due to his construction of Harrenhal. We’ll get to that later.

He was hated by almost everyone because of how vain and cruel he was. His tactics were so awful that he gained a reputation throughout all of Westeros, not just the areas he ruled. Harren Hoare exhausted both the Riverlands and the Iron Islands to build his monument. Rather than paying people to build Harrenhal for him, he chained slaves to sledges or let them die in the stone quarries. When one slave died, they were replaced with a fresh body -- and on and on that went until construction was complete. Rumor has it there’s a lot of blood mixed in with the stone used to build Harrenhal.

12. It had a legendary godswood

Game of Thrones Weirwood Tree

The godswoods of Westeros are usually associated with the North and the Starks, who still worship the old gods. However, there used to be godswoods across the continent before they were either cut down or burnt by followers of the Seven. There are still a few in the south, and one of the most significant is on the Isle of Faces -- the island in the middle of the Gods Eye lake.

The godswood on the Isle of Faces covers twenty acres of land. This is especially impressive considering that Harren Hoare cut down many of the weirwood trees in order to build Harrenhal. Although the faces of most weirwood heart trees aren’t exactly pleasing to behold, the Harrenhal heart tree is terrifying. Its face is as cruel as the godswood’s former ruler, with a twisted face and glaring eyes. There are thirteen marks carved into it from a previous battle, and they still bleed every spring.

11. It was the center of the Hoares’ opposition to Aegon Targaryen

Aegon the Conqueror wileding Blackfyre in battle in The World of Ice and Fire.

When Aegon the Conqueror first began his takeover of Westeros, Harren Hoare had just moved into the freshly completed Harrenhal. He laughed at Aegon when he showed up outside of the gates. He had just finished building a castle that no man or army could take down -- why should he be afraid of someone outside of his fortress?

He was partially right. There wasn’t a man or army who could defeat Harrenhal alone. But Harren Hoare had forgotten a pretty crucial detail: the Targaryens have dragons. Big ones.

The fire from Aegon’s dragon Balerion was strong enough to melt stone, and King Hoare was burned alive in Harrenhal along with his sons. The entire Hoare line was extinguished that day, and Aegon Targaryen became ruler of the Riverlands and Iron Islands simultaneously. The building has never been able to be repaired, and while it still stands, the entire structure is still partially melted from dragonfire.

10. Daemon Targaryen attacked it to kick off the Dance of Dragons

Aegon Targaryen Attacks Harrenhal Game of Thrones

As if melting half of the building wasn’t enough, Harrenhal was attacked by the Targaryens again roughly 130 years later. This fortress can’t catch a break.

Prince Daemon Targaryen was one of the most skilled warriors in the Dance of Dragons, also known as Westeros’ civil war. He was both the uncle and husband of Rhaenyra Targaryen, whose claim to the throne he was supporting. (Remember that Targaryen tendency towards incest? It’s not just the Lannister twins!) Since House Tully was sitting this war out, Prince Daemon figured that Harrenhal would be a great place to rally the troops. One problem with that -- the current lord of Harrenhal, Larys Strong, supported Rhaenyra’s opponent, Aegon II Targaryen.

All Prince Daemon had to do was fly his dragon to the top of the tallest tower. Lord Strong, remembering how Harrenhal’s towers were melted in the first place, surrendered almost immediately. Easiest conquest ever.

Aegon II’s soldiers eventually retook Harrenhal, but no one is quite sure what happened to House Strong.

9. There are five towers, all with their own legends

Harrenhal ruins in Game of Thrones

The towers of Harrenhal are all distinctly named and have their own legends and lore to go with them. The original names were lost after Aegon’s dragon burned Harrenhal to a crisp, but the five names that persist in the Game of Thrones world we know are the Tower of Dread, Widow’s Tower, Wailing Tower, Tower of Ghosts, and Kingspyre Tower.

The names make it slightly easy to guess the history or rumors that accompany each tower. Kingspyre Tower, for example, is where Harren Hoare died when his fortress burned. The successive lords or castellans of Harrenhal have lived there since. A stone bridge connects it to Widow’s Tower, underneath of which is a huge cell for prisoners. The Wailing Tower is named for the noise you hear when the wind blows from the north. The Freys lived here after Roose Bolton reclaimed the castle.

The Tower of Dread is where the northmen were held prisoner, while the Tower of Ghosts is closest to the sept and the most ruined of the five towers.

8. It took 40 years to build

Harrenhal Game of Thrones

It’s either funny or tragic that the famous ruins originally took forty years to build. Given the building’s size and the physical limitations of the people constructing it, this time frame makes sense. After all, its stables alone can fit a thousand horses, and its curtain walls are apparently roughly as tall as a mountain cliff.

After all of the tragedy and pain that went into building it in the first place, House Hoare didn’t even get to enjoy it in its intended state. The very day that Harren Hoare moved into his cavernous new home, Aegon Targaryen came knocking at the door with dragons. Hoare literally had less than a full day to live in his fortress. Given that only a third of Harrenhal is occupied at once due to the cost it takes to maintain it, we can guess that he only actually saw a tiny portion of what took forty years to create.

7. People believe it’s cursed

Mad Lady Lothston Game of Thrones

The constant tragedy that afflicts Harrenhal has given it a reputation in superstitious Westeros. People now believe that the whole place is cursed, and for good reason.

Countless numbers of people died while Harrenhal was being constructed, and some say that Harren Hoare mixed their blood into the mortar. There's literal blood in the walls of the fortress, and that never bodes well. Many say that the whole place is haunted, especially the Tower of Ghosts. There are a few stories in particular that are told frequently that the Stark children learned from Old Nan. Mad Lady Lothston was said to send a giant bat to snatch children for her pot. Others claim that the ghosts of Black Harren and his sons still walk the halls, with the flames that killed them surrounding their silhouettes. Meanwhile, some servants go to sleep and are never seen or heard from again.

To make matters worse, no one can seem to keep a hold of the place.

6. It’s been held by more than six different houses

Black Flag Harrenhal Game of Thrones

After House Hoare was destroyed, the Targaryens didn’t keep Harrenhal. While the dragons settled in at King’s Landing, House Qoherys was granted Westeros’ largest fortress. House Qoherys held it for thirty-seven years before Harren the Red, who claimed to be Black Harren’s lost grandson, took it back. It was short-lived -- as soon as he had killed all of the men in the castle and named himself lord, he went back to being a bandit.

Harrenhal would later be held by Houses Harroway, Towers, Strong, and Lothston. In keeping with the rumors of the curse, each house died out a few generations after claiming Harrenhal.

No one seems to be able to hold it for long, not without some sort of tragedy befalling them. Since 298 AC (the beginning of Game of Thrones), Harrenhal has been held by nine different individuals. Even for wartime, that’s a lot of turnover for a massive castle.

5. It’s held by House Whent at the start of the series

Game of Thrones Season 6 Return to Riverrun

At the beginning of both the show and the books, Harrenhal is held by House Whent. They were the last true owners of the house, which could become important as the story moves forward.

The Whents were the seventh noble house to rule Harrenhal, and they ruled the castle for three generations. They were originally knights for the Lothstons, but when Lady Lothston became Mad Lady Lothston, the Whents defeated their liege lords for the Targaryens and received Harrenhal in return. It is Lady Shella Whent who holds it at the beginning of Game of Thrones and surrenders it to Tywin Lannister when he claims it for his army. She’s presumed dead.

House Whent is a house of the Riverlands, and a fairly young one at that. Their line doesn’t go back nearly as far as a house like Lannister or Stark, but they still had a major impact on the Seven Kingdoms when they chose to host a massive tournament during the reign of the Mad King.

4. It hosted the tournament that helped set off Robert's Rebellion

Rhaegar Lyanna Artwork by Mathia Arkoniel A Song of Ice and Fire

It’s difficult to imagine a time when Westeros was peaceful, but when Ned Stark and Robert Baratheon were young lords, there was indeed peace...kind of. Although the country wasn’t at war, the rule of the Mad King meant that everyone lived under constant threat of violence.

Lord Walter Whent hosted a humongous tournament where lords and knights came from across the country to compete. It was organized to celebrate his daughter’s nameday, and she was supposed to be named the queen of love and beauty. During the ten day tournament, rumors flew that Rhaegar Targaryen was plotting to overthrow his unstable father, Jaime Lannister was named to the Kingsguard, and Prince Rhaegar won the joust. He ignored Lord Whent’s daughter and instead named Ned Stark’s sister Lyanna as the queen of love and beauty. Fans who subscribe to the R+L = J theory (that Jon Snow’s real parents are actually Rhaegar Targaryen and Lyanna Stark, one that's at least been confirmed in the show) see the Tourney at Harrenhal as the potential beginning of their relationship.

Of course, the events that immediately followed that tournament (Rhaegar "kidnapping" Lyanna, the Mad King executing Ned Stark's father and older brother, Robert Baratheon and Ned rebelling against the crown and overthrowing the Targaryens) may ring a bell or two.

3. It appears in an Easter Egg reference in the season 4 finale

Harrenhal Easter Egg Game of Thrones

There’s not enough time for the show to include all of the backstory that George R.R. Martin has written for his series. However, the team behind Game of Thrones does a fantastic job of weaving information into the background of certain scenes, so that viewers really feel like they’ve been dropped into a world that’s existed for centuries.

One example of this comes in the season four finale, when Jaime is looking through the Book of Brothers. He wants to see how he will be remembered as a member of the Kingsguard, so he flips through the pages of the book to find his own. If you pause at the right place, though, you will see Harrenhal -- specifically, the Tourney at Harrenhal -- mentioned on one of Ser Barristan Selmy’s pages.

It’s enough to make you wonder just how important that tournament will turn out to be in seasons seven and eight.

2. Almost every individual who has held it since the start of ASOIAF has died

Littlefinger looking down with a serious expression in Game of Thrones.

After Shella Whent gave up Harrenhal to the Lannisters, she passed away. Tywin named Janos Slynt as Lord of Harrenhal for his help in betraying Ned Stark. Slynt was later stripped of his title and sent to the Wall, where he was executed.

Tywin Lannister himself took control of Harrenhal after that, and...well, we all know the crappy way he died. Amory Lorch, who was named castellan, was fed to a bear. Roose Bolton also held Harrenhal. Although he's still alive in the books, on the show, he was murdered by his own son, Ramsay. Vargo Hoat, Gregor Clegane, and Polliver have also all held Harrenhal for a short time, and they were tortured, stabbed by a poisoned spear, and killed in an unknown manner, respectively.

That just leaves Petyr Baelish, who was named Lord of Harrenhal after the Battle of the Blackwater in A Clash of Kings...even though Roose Bolton held it at the time. At the moment, he’s still alive in both the books and on the television show -- but if what’s happened to everyone else is any indication, he might have to fight a little harder to stay that way.

1. The Starks can claim Harrenhal through blood

House Stark Sigil from Game of Thrones

Jon and Sansa reclaimed Winterfell at the end of season six, but the Stark family could actually add one more castle to their holdings -- Harrenhal. And they may not even have to fight that hard for it.

We mentioned earlier that House Whent holds Harrenhal at the beginning of the series. Lady Minisa Whent married Hoster Tully, Lord Paramount of the Trident. The couple had three children: Edmure, Lysa, and Catelyn. Catelyn Tully, of course, would go on to marry Ned Stark.

Given that Lady Shella Whent was the last of her line and is presumed dead, by blood, Harrenhal could go to the Starks. Although Harrenhal’s history says that no lord can keep it for long, it was originally meant for a king. Jon Snow was named the King in the North, and kingsblood runs through the veins of all the Stark children. If certain fan theories are right, maybe the Starks can finally break the Harrenhal curse.

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Season 7 of Game of Thrones premieres on Sunday, July 16 on HBO.