The Grand Underground is a massive, well, underground area located beneath the Sinnoh region. Think of it as Brilliant Diamond and Shining Pearl’s very own Wild Area. It contains multiple smaller zones where you can capture many Pokémon (including rare ones), meet other players, and trade items with NPCs. The Grand Underground is also where you can set up your Secret Base.
How to access the Grand Underground Pokémon Brilliant Diamond and Shining Pearl
You can visit the Grand Underground by using the Explorer Kit's key item. Players can receive it from the Underground Man in Eterna City. His house is located beside in Eterna City's Pokémon Center.
Related: How to get the Bike in Pokémon Brilliant Diamond and Shining Pearl
Once you have the Explorer Kit, you can fall into the Grand Underground from anywhere as long as it’s an outdoor location. Its use is similar to the bikes. The area you fall into depends on where you use the Explorer Kit on the Sinnoh map. You can exit the Grand Underground by pressing Y.
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Bianca Versoza is Pro Game Guides' Weekend Editor. With over three years of experience in gaming journalism, she specializes in anything remotely turn-based and strategic, like Pokémon, Valkyria, and Honkai: Star Rail. Bianca is a huge fan of Square Enix, RPGs, party games, and visual novels, but will play anything with a banger OST. She's a proud early bird.