The Grand Underground is a vast network of tunnels beneath Sinnoh, accessible with the Explorer Kit (received from the Underground Man in Eterna City). It offers several unique activities:
- Digging for Treasures: Use your pickaxe and hammer to dig up valuable items like evolution stones, fossils, and spheres. Spheres can be traded for goods or used to decorate your Secret Base.
- Secret Bases: You can create your own Secret Base and decorate it with statues. Statues influence the types of Pokémon that appear in the Underground's Pokémon Hideaways.
- Pokémon Hideaways: These are special caves where you can find Pokémon not typically found in the overworld, including some rare species. The types of Pokémon that appear are influenced by the statues in your Secret Base.
- Traps: Set traps to catch other players (in multiplayer) or to find items.
The Grand Underground is an excellent way to find rare items, train your Pokémon, and collect unique species. Spend time exploring its depths!