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Pokemon Brilliant Diamond & Shining Pearl Grand Underground guide: digging, Diglett hunting, items, encounters & more

by Alex Donaldson on 20 November, 2021

One highly anticipated returning feature in Pokemon Brilliant Diamond & Shining Pearl that's been significantly expanded in the new Nintendo Switch remakes of the DS classics is the Grand Underground - a sprawling network of mines that also heralds the return of the fan-favourite Secret Bases for Pokemon trainers to decorate.

As well as being a place for trainers to live - because who doesn't want to live in a dark cave full of hostile monsters - the Great Underground is also a vital piece of the meta of Pokemon Diamond & Pearl. It's home to the digging mini game, which lets you get rare items, and Pokemon Hideaways and Nests which can be used to farm or find the rarest critters you're after. Thanks to a new mechanic, you can even use the Grand Underground to shiny hunt.

On this page, we explain the Grand Underground, how to access it, and everything that you can do there. Scroll, or hit a link to go to the relevant section:

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How to access the Grand Undeground in Pokemon Brilliant Diamond & Shining Pearl

Given that it's a major feature of the games, the Grand Underground will be introduced to you naturally as you progress through the Sinnoh-based adventures of Pokemon Diamond and Pearl. Eventually, in Eterna City, you'll be given an Explorer Kit - and that's everything you'll need to go spelunking in the underground.

In the new Nintendo Switch versions of the game, the Grand Underground has undergone a significant expansion -  and is now split into six different areas, each accessed from a different part of Sinnoh. 

Specifically, you can access the six different Grand Underground areas from Twinleaf Town, Eterna City, Celestic Town, Snowpoint City, Sunyshore City, and from the area unlocked after beating The Elite Four. 

Each of these areas has its own uinique biome, which in turn impacts the Pokemon encounters found in the Underground beneath. 

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How to make a Secret Base in the Grand Underground

Returning in this version of Pokemon Diamond and Pearl are secret bases - but as with much of the Underground, this has been expanded. In order to create a secret base, you'll need a Digger Drill item, which can be purchased from the shopkeepers around the Grand Underground's tunnels in exchange for Spheres.

The Digger Drill will set you back up to 20 spheres - and you can gather spheres by participating in the digging mini-game, which we explain below. You have everything you need to dig from the moment you can first access the Underground, meaning all you have to do in order to create a Secret Base is farm some spheres and pick a spot.

Once the Secret Base is set up, other players will be able to visit it through the online functionality. You can then also decorate your Secret Base area with statues and other items. The items that adorn your secret base can have wide-reaching effects; specifically, any Pokemon you have raises the chances of encountering Pokemon of their same types in the Underground. You can have up to 18 statues, and the boost stacks. 

Doubling Shiny Encounter Rate with Diglett Hunting

One major feature in the Grand Underground, and new to Brilliant Diamond and Shining Pearl, is the appearance of special Diglett and Dugtrio across the Grand Underground. They'll generally appear where the different paths of the Grand Underground intersect, but they'll make a swift getaway before you can get too close to them. That's okay, however: your goal isn't to catch them.

Each time one of these critters retreats, they'll leave behind some energy of between 1 and 3 points. If you collect 40 points in an Underground trip, you trigger a bonus: immediately after picking up that 40th point, your shiny encounter rates will dramatically increase - in fact, they'll double!

The chance of catching a Shiny Pokemon in Diamond and Pearl is 1 in 4096, the same as in every other game in the series. But with the Diglett bonus, the shiny chance is slashed to 1 in 2048. Additionally, your chances of getting better loot from digging are also enhanced in that same time period.

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Pokemon Encounters & Nests in the Grand Undeground

The shiny rate boost in the Grand Underground is of course only as useful as the Pokemon you can find there - but luckily, the spawn list of Pokemon in the Underground is seemingly quite extensive. 

First of all, you'll be able to find plenty of the Pokemon that are exclusive to your version of the game in the Undeground. That means Brilliant Diamond players can catch the likes of Scyther, Ekans, Murkrow and Solrock down in the Underground - and also find the fossil to revive Cranidos. Menawhile, Shining Pearl players can likewise access Vulpix, Sandrew, Lunatone and Teddiursa, as well as the fossil required to revive Shieldon.

Beyond that, the Pokemon Hideaways mechanic, which is new for the Switch Remake of the game, allows you to catch many Pokemon, some of which exclusively appear in this hideaways. Hideaways are set up as 'biomes', meaning they'll have an environmental theme with Pokemon spawns to match. 

The exact Pokemon available via hideaways grows as you progress through the game - but by the time you unlock the National Pokedex, most of the Pokemon in the game can be accessed this way. You can even manipulate the spawns slightly based on what statues are placed in your Secret Base.

Digging in the Grand Underground

The Grand Underground is basically a great big mine that runs beneath the Sinnoh region where Pokemon Diamond and Pearl take place, and that means it only follows that you'll spend at least some of your time... Digging. Thie action allows you to mine out items from the Grand Underground, with the loot you're able to obtain very useful in your quest to become a Pokemon Master.

You'll get a hammer and a mallet as part of your Explorer Kit, and you can use this to chisel at the walls of the Grand Underground in order to dig out useful loot. 

To dig, all you need to do is go up to one of the diggable spots and interact with it in order to activate a mini-game. If you're struggling to find the Digging spots, they're highlighted on the map and can also be seen by using the radar that's mapped to R; this highlights them for you.

Once you're in digging, it takes place in a mini-game where you use the Red Hammer and Blue Chisel to knock out elements of the wall. You have a limited number of hits, and heavier rocks require more attempts to break through. Hidden beneath each digging board will be a variety of items - but you only get to keep those you've fully uncovered. There's a level of strategy to this, and you'll want to carefully try to aim for the rarer items first by trying to locate all the items quickly first, then digging out those you want the most.

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Items Available in the Grand Underground

Through digging and more conventional means, you'll be able to farm a variety of helpful items in the Grand Underground. This is a great place to get a bunch of different items, including some of the ones that are more rare and limited out in Brilliant Diamond and Shining Pearl's overworld naturally, including this game's Pokemon evolution stones. 

First of all, there's the Spheres you can get. Spheres can be traded with NPCs to get other items, or expand the size of your secret base. Here's the different types of Sphere encountered in the Underground:

  • Red Sphere S or L - "A red sphere that glows like fire."
  • Blue Sphere S or L - "A blue sphere that glistens like ice."
  • Green Sphere S or L - "A green sphere that glows like sunlit leaves."
  • Prism Sphere S or L - "A small sphere that's clear enough to see through."
  • Pale Sphere or L - "A small sphere that glows in seven colors."

Next, there's a variety of regular items you can find in the Grand Underground, making it a great place to obtain certain key items that are otherwise difficult to find in Pokemon Diamond and Pearl. Here's a full Grand Underground Item List:

  • Evolution Items:
    • Sun Stone
    • Moon Stone
    • Fire Stone
    • Thunder Stone
    • Water Stone
    • Leaf Stone
    • Oval Stone
    • Everstone
  • Shards:
    • Red Shard
    • Blue Shard
    • Yellow Shard
    • Green Shard
    • Mysterious Shard S / L
  • Fossils:
    • Root Fossil
    • Claw Fossil
    • Helix Fossil
    • Dome Fossil
    • Old Amber
    • Armor Fossil (Shining Pearl only)
    • Skull Fossil (Brilliant Diamond only)
  • Generic Items:
    • Revive
    • Max Revive
    • Odd Keystone
    • Star Piece
    • Heart Scale
    • Rare Bone
  • Pokemon Hold Items:
    • Light Clay
    • Iron Ball
    • Icy Rock
    • Smooth Rock
    • Heat Rock
    • Damp Rock
    • Hard Stone
    • Flame Plate
    • Splash Plate
    • Zap Plate
    • Meadow Plate
    • Icile Plate
    • Fist Plate
    • Toxic Plate
    • Earth Plate
    • Sky Plate
    • Mind Plate
    • Insect Plate
    • Stone Plate
    • Spooky Plate
    • Draco Plate
    • Dread Plate
    • Iron Plate
    • Pixie Plate