Like someone who buys a Ferrari just to take the kids to school, the Winchester brothers have been massively under-utilizing their Bunker in Supernatural. Returning from an extended pandemic break, Supernatural season 15 picks up with Sam and Dean Winchester trying to fix their creaking home. Unable to call a regular plumber to their top-secret HQ, the boys set to work themselves, and hit "Reset" on the Bunker's control room to try and kick the electrics back into life. Instead, they unleash a Wood Nymph who was secretly locked within the Bunker's walls, and this mysterious character, affectionately known as Mrs. Butters, teaches the boys many secrets about their home.
During the first few seasons of Supernatural, the Winchester brothers lived on the road, moving from motel room to motel room in their iconic Impala chasing down monsters to kill. In Supernatural season 8, Sam and Dean discover that they are the last living legacy members of an ancient anti-paranormal organization called the Men of Letters. As the only remaining successors, the Winchesters inherit "the Bunker" - the Men of Letters' base of operations. Covered in warding to keep out enemies, the introduction of the Bunker changed Supernatural by adding a regular setting. The bunker is also packed with magic ingredients, ancient artifacts and helpful tomes, and made the lives of Sam and Dean Winchester infinitely more comfortable.
In Supernatural season 15's "Last Holiday," however, Mrs. Butters reveals the true power of the Bunker. According to the enthusiastic housekeeper, the Winchesters have been using the Bunker on "standby mode" right from the start, limiting the power of its warding and removing many of the most useful features. When Dean hits the big reset button, the power of the Wood Nymph is infused with the Bunker, giving the Men of Letters' HQ a major upgrade. As well as presumably boosting the warding, the giant map table in the center of the main atrium (usually reserved for housing laptops and beer bottles) acts as a "monster radar" which tells the Winchesters where villains are hiding and what to expect. This feature proves invaluable throughout the episode, and Dean was livid at not discovering the handy paranormal Tinder sooner.
Supernatural fans would've already noticed the giant telescope at the rear of the Bunker, although the contraption itself is never used. When activated, Mrs. Butters reveals this to be an inter-dimensional geoscope, and although she doesn't explain the details, the title suggests Sam and Dean could've used this feature to peek into other dimensions. If only they knew about this when dealing with Michael and the Apocalypse World.
Unfortunately, Mrs. Butters takes exception to playing butler for the son of Lucifer, and after the Winchesters discover the Nymph was forcibly captured by the Men of Letters, the cheerful woman is relieved of her duties to return to the wild. Without her magic, the Bunker reverts to standby mode, and the invaluable new perks are once again lost. Nevertheless, it's fascinating to know that Sam and Dean had both a radar system and a looking glass into parallel worlds right next to them the entire time. And perhaps if Mrs. Butters have been awoken before Jack was born, she and the Winchesters would've never fallen out, meaning Sam and Dean could've kept the Bunker's upgraded systems. The Winchesters might've even employed their own Wood Nymph to help jazz up their home.
"Last Holiday" was an entertaining bottle episode that did little to advance the central story of Supernatural season 15, but the story did answer several long-standing Bunker mysteries ahead of Supernatural's series finale. Fans now know the purpose of the eternally-unused telescope, as well as the map table that Sam and Dean have always just used as a regular desk. The resolution of these mysteries, as well as the Winchesters celebrating all of their missed holidays, perhaps teases an unhappy conclusion to Supernatural as the upcoming battle with God looms.