A chasm in the northern part of Pyrite Town allows sunlight to reach parts of The Under. This same chasm also separates The Under into two halves: the northern half, which is home to both Colosseums, and the southern half, the home of most of the city's commercial establishments. A UFO operated by Disks connects the two halves.
It was originally an artificial town constructed for the convenience of the miners of Pyrite. Instead of having to commute between Pyrite and the mine each day, the workers assigned to dig in the mine would stay in The Under instead. When the mine closed, the miners chose to remain in their adopted home. Now, most of The Under is populated by the descendants of the original mining crew. The original inhabitants that still live in The Under are quite old, but are fond of telling stories of when the mine was in its prime.
Since The Under is a full-fledged city in itself, many of its inhabitants have rarely, and in some cases never have, been to the surface. It is for this reason that the residents tend to be suspicious of those visiting from Pyrite. A fenced-off area in the southeastern portion of The Under serves as the town's makeshift prison; it is in this structure that visitors from the surface are occasionally detained.
In Pokémon XD: Gale of Darkness, The Under is completely inaccessible because it had been buried due to the incident with Cipher, as villains like Lady Venus could use The Under to hide out. The former residents have since moved to new homes in Pyrite Town and Gateon Port.
The lone Herb Shop in Pokémon Colosseum is located to the west of the Under Colosseum on the northern edge of the chasm. Like other Herb Shops in other regions, it sells inexpensive herbal medicine that will lower the friendship of Pokémon that consume it.
The Junk Shop is located in the south-central portion of The Under, which serves as The Under's commercial district. The shop is little more than a mechanics garage owned by an old man, who was said to be a brilliant engineer when The Under was in its prime.
The Kids Grid is a television network that is known for its opposition to Cipher. Their headquarters are located in the western portion of The Under on the southern edge of the chasm. Not far to the south is the large satellite dish used by the Kids Grid to transmit data.
A television studio is located to the east of the Under Colosseum on the northern edge of the chasm. It was used by Venus to broadcast her show, "Under Time", until she was defeated by Wes and Rui. It is connected to both the Under Colosseum and The Under Subway by a pair of basements.
The Under Grand Hotel
The Under Grand Hotel is located in the heart of The Under's commercial district. A one-night stay at the hotel costs 1,000. Above the hotel is a bar frequented by some of The Under's more seedy members. If the player walks behind the counter and speaks to the clerk, he will not offer a night's stay, fearing that the player plans to rob him.
The Under Subway is a former mining railroad that was renovated by Cipher for the purpose of transporting Shadow Pokémon between The Under and the Shadow PKMN Lab. The tram car that runs along the line is known as the Shadow Liner. An R-Disk is initially required to access the subway; however, once the door connecting the Under Colosseum to the basement of Venus's former studio is unlocked, it is possible to reach the subway without any Disks.
The Under Colosseum is located in the north-central portion of The Under. It has a built-in Pokémon Center as well as a mine shaft that leads to a point on the surface just northwest of Pyrite Town. This mine shaft can be used to quickly commute from The Under to anywhere in Orre, and vice versa, once it is used from the Under Colosseum side. An F-Disk is required to initially access the Colosseum. However, once the player has used the exit elevator in the Colosseum's lobby, it can be accessed without any Disks.
Trainers with a Poké Ball by their names may be challenged for a rematch after defeating certain bosses. In a rematch they may have higher-level Pokémon, and any Shadow Pokémon previously caught will be replaced.