Pokémon Diamond and Pearl/The Underground

The underground contains similar aspects of Spectrobes in it. This is because you can scan the ground with your Stylus, and you can locate sparkles on the ground. If they are in a wall, you can dig them up and exavate colored orbs. Orbs come in several different colors; red, blue, green, and yellow. There are also treasures such as Prism Spheres or rare Diamond and Pearl Items, such as Moon Stones, Thunderstones, and Heart Scales. If the sparkle is just on the ground, do not step on it as it mey be a trap. Instead, go to the square in front of it and press. You will disengage the trap and you can set it wherever you wish. The other thing a sparkle on the ground could be is a buried Sphere.

You also have a radar on the top screen that tells you where hidden objects are. They appear all the time as little sparkles on the radar.

You can also make Secret Bases in the Underground, which are very similar to those from Pokémon Ruby and Pokémon Sapphire. Unlike Ruby and Sapphire, however, you must obtain a Digger Drill from the Underground Man or trade for one in the Underground. Once you do this, go to "Traps" and use your Drill on a wall space. Once you do this, the Drill will break, and if you want to move your Base you'll have to aquire a new one.

You can also decorate your Secret Base. You can put up to 15 items at a time in your Base, and if you want different ones you'll have to switch out a few items. You can get decorations from three different places: the Underground Man, the Veilstone Department Store, or the Battle Tower. The Underground Man gives you a few basic items once you create a first Secret Base with the Digger Drill he gives you. You can buy unlimited copies of decorations from the Veilstone Department Store, and You can get trophies for beating certain amounts of trainers in a row at the Battle Tower.

There are several items that are obtainable in the underground, but they can be grouped into three categories: Fossils, Treaures, and Spheres.

Spheres
Spheres are the most common items in the underground. They can be obtained by excavating them when you dig into a wall. Almost every single wall contains at least one Sphere.

You have a limit to how many Spheres you can carry (about 20), so obviously you will have to get rid of some. However, you can do something more worthful than just throwing them away. You can bury them in the ground, and they will grow in size every day. if you wait several days, even the tiniest sphere can be turned into a size 60 or larger!

Fossils
Fosslis are very rare items in the Underground that can be turned into level 20 Pokémon at the Coal Mining Museum in Oreburgh City. It will take a day for the scientist to turn it into a Pokémon.

Treasures
Treasures are rare items in the Underground that can be put into your Bag in the overworld. They can be items to sell, rare Type-boosting items, or rare weather-prolongers.

Flags
The Flags are obtainable from other players' Secret Bases, at their PCs. Obtaining a flag greatly boosts your Underground score, plus obtaining enough flags gains you upgrades for your Secret Base.