One of the more memorable side areas to visit in the original Pokémon Diamond and Pearl was the Underground, an expansive area beneath Sinnoh accessible after getting your second Gym Badge. You could excavate the walls for treasure, such as spheres, evolutionary stones, plates, and more, and you could also set up traps for other players playing over local wireless. Despite Pokémon Diamond and Pearl being the first main series games to offer online play, this feature was restricted solely to local play.
Pokémon Brilliant Diamond and Shining Pearl have drastically revamped the whole Underground, though, and have reintroduced it as the Grand Underground, and it’s still accessible by using the Explorer Kit item received in Eterna City.
From the prerelease information, it appears to be quite similar to the original Underground, but also different in quite a few ways. Below is a look at some of the features in the Grand Underground along with some observable differences with the original Underground for comparison.
Online and Local Wireless
Before continuing to talk about its features, the official website confirms that the Grand Underground is available both with local wireless communication and with online communication (the latter presumably requiring a Nintendo Switch Online membership, however).
This is great news as it was a lot of fun to be able to wander around the vast expanses of the Underground with friends or even people in the area you didn’t know. You could lead friends to your base or lead your enemies to traps you set around to mess with them.
Regrettably, there appears to be no indication that traps will be returning to the Grand Underground, so that part of the old Underground appears to be left in the past, but with it effectively serving as the Brilliant Diamond and Shining Pearl equivalent of the Wild Area—an area in Pokémon Sword & Shield that players from all the world could see each other roaming around—this is likely an unavoidable evolution of ensuring that the game can be fun for everyone and players don’t have to worry about getting stuck anywhere in the Grand Underground.
That being said, it does mention that players will be able to dig for Fossils together in the Grand Underground, so it will likely be beneficial to have some assistance while digging and exploring and still provide a fun experience.
Mining For Treasure
As with the original games, one of the main things to do in the Grand Underground is mine for treasure! On the Grand Underground map, you’ll see little sparkling nodes pop up, and you’ll have to run over to their general location in order to deduce where to mine. At that point, you can tap on the touch screen (presumably; there might also be a button for docked players) and that will activate the radar, which will reveal any active veins of treasure in the walls and show them as little sparkling spots.
Approach any of these sparkling spots and interact with them to start the digging minigame, where you will need to carefully unearth treasures hiding in the walls. You can smack at the walls with the sledgehammer tool to break larger areas and tougher surface rocks but also fill your mining bar (large crack at the top of the screen) faster, or you can use the pickax to excavate smaller portions accurately and without raising that bar as quickly.
Finding a good balance of these two approaches will be key, at least if it is anything like the original in Diamond and Pearl.
You can find all sorts of treasures down there, such as Spheres—items that can be traded for, well, presumably for things like statues or items, although this is not yet confirmed—in addition to helpful items like evolutionary stones, fossilized Pokémon, and more. The official website mentions that Pokémon statues can be found while mining as well.
One major new addition to the Grand Underground is Pokémon Hideaways. Pokémon Hideaways are completely new underground areas that you can encounter Pokémon in, including some Pokémon in the Sinnoh region that can only be found in Hideaways.
These Hideaway zones appear on the Grand Underground map in the top-left corner as rooms with a large “?” on it. Most of the Hideaways are smaller, but each section of the Grand Underground has a large room with that question mark in it.
The wild Pokémon that appear down in the Hideaways can be affected by the different Pokémon Statues that you decorate your Secret Base with.
Some of the more interesting Pokémon found in the Hideaways include Houndoom and Swinub (not in the original Diamond and Pearl Sinnoh Pokédex), as well as a few others like Skorupi, Croagunk, Roselia, Pelipper, Bibarel, Buneary, Bronzor, Mr. Mime, and more that were already available. Munchlax can also be found down there, which is very welcome, as it was a notoriously difficult Pokémon to obtain in the original games.
Some of the screenshots from the game show other players in these Pokémon Hideaways. What purpose they have there or what benefit they offer is currently unknown, though.
Secret Bases and Pokémon Statues
One of the cool things from the old games was the ability to create a Secret Base inside of any of the walls in the Underground and then decorate it with various decorations that you could acquire in exchange for Spheres mined in the walls. You’ll need to have an item called the Digger Drill in order to drill into the walls of the Grand Underground and form your Secret Base.
Although mining will still earn the player Spheres in a similar fashion, footage and screenshots of the Secret Bases in action seem to suggest that decoration of the Secret Base is limited to just Pokémon Statues.
There are statues of all sorts of Pokémon, including Turtwig, Chimchar, Piplup, Pachirisu, Snorlax, Gyarados, Floatzel, and even special jade statues of Charizard and Venusaur. These statues don’t just look cool—they also boost the chances of certain types of Pokémon appearing in the Pokémon Hideaways, such as increasing the chances of Water-type Pokémon appearing.
Thankfully, it looks like you’ll be able to place plenty of statues in your Secret Base: prerelease footage showed an indicator saying “Statues placed: 2/18” while arranging statues in the base, so whether this is a hard limit or based on the size of the room, it’s still indicative of a good amount.