Pokémon: Shining Pearl and Pokémon: Brilliant Diamond both include a unique area known as the Grand Underground where players can hunt for treasure and build secret bases. In the original games, there were six regions in the Underground that were accessed through various points in the overworld using an Explorer Kit. There are a few changes to this area in the remakes.
The Underground updates in Shining Pearl and Brilliant Diamond are minor and serve to modernize the area. Rather than a square layout, the Grand Underground matches the layout of the landmass that it's beneath, so the six separate regions are different in both size and shape. The Grand Underground now includes Pokémon Hideaways where wild Pokémon can be encountered. The addition of Pokémon Statues in digging minigames serves to replace Goods as the sole decoration for Secret Bases. It is currently unknown if there are any other additions or exclusions from the original Underground region and its mechanics.
To access the Grand Underground, players will need to obtain an Explorer Kit from the house next to the Pokémon Center in Eterna City. Reaching Eterna City requires that players help a young child in Floaroma Town save their father and travel through Eterna Forest, beating members of Pokémon's Team Galactic along the way. Once in Eterna City, players will be able to acquire the Explorer Kit, but there are different areas of the Grand Underground to enter depending on where the item is used.
Accessing the Grand Underground in Shining Pearl and Brilliant Diamond
The Grand Underground in Shining Pearl and Brilliant Diamond is still split into six regions: Northwest, Northeast, Southwest, Southeast, Small Center, and Large Center. Using the Explorer Kit in different areas of the overworld, players can access each area to complete digging minigames, build secret bases, and explore the new Pokémon Hideaways. Each region in the original games had set access points correlating to Underground regions:
Northwest
- Fullmoon Island, Acuity Lakefront, Lake Acuity, Newmoon Island, and Snowpoint City
Northeast
- Fight Area, Battle Park, Flower Paradise, Stark Mountain, Survival Area, Seabreak Path, and Resort Area
- Routes: 224 through 230
Southwest
- Verity Lakefront, Lake Verity, Fuego Ironworks, Valley Windworks, Twinleaf Town, Jubilife City, Oreburgh City, Canalave City, Sandgem Town, and Floaroma Town
- Routes: 201, 202, 203, 204, the southern part of 205, 206, 207, and 218 through 221
Southeast
- The southern part of Sunyshore City
- Routes: 222 and the southern region of 212
Small Center
- Spear Pillar
- The summit of Mount Coronet
Large Center
- Hearthome City, Solaceon Town, Solaceon Ruins, Velistone City, Celestic Town, Eterna City, Pastoria City, the northern part of Sunyshore City, Pokémon League, Iron Island, Spring Path, Sendoff Spring, Turnback Cave, Eterna Forest's exterior, Valor Lakefront, and Lake Valor.
- Routes: 208, 209, 210, 211, 213, 214, 215, 216, 217, 223, and the northern part of 205 and 212
There is currently no indication that these entrance points will change in Shining Pearl and Brilliant Diamond. Players simply need to use their Explorer Kit in one of the above areas to gain access to the Grand Underground. Once beneath the Sinnoh region, players can explore, mine fossils, dig for Pokémon Statues, encounter wild Pokémon in Hideaways, and build Secret Bases. The Grand Underground is one of the many features included in the new Pokémon: Shining Pearl and Pokémon Brilliant Diamond.
Pokémon: Shining Pearl and Pokémon: Brilliant Diamond will release on November 19th, 2021 for Nintendo Switch.