From Bulbapedia, the community-driven Pokémon encyclopedia.
Altru Tower (Japanese: アンヘルタワー Ángel Tower) is a location in Pokémon Ranger: Shadows of Almia. It is the last location in the game's storyline and also the location of the special mission, Liberate the Tower.
Team Dim Sun uses Altru Tower as a cover for their ultimate weapon, the Incredible Machine. The weapon is a giant Gigaremo that is powered by the Shadow Crystal.
The tower's interior is made up of seven floors. The second, third and fourth floors play host to three generators for creating a barrier to guard the tower's peak. The generators, colored respectively in yellow, red and blue, are guarded by the members of the Sinis Trio. On the fifth floor, special black Gigaremo units restrain a mysterious shadow that is actually Darkrai. The sixth floor only contains a Save Machine and the stairs to the roof.
Altru Tower's roof is where the Shadow Crystal is located and is where the final battle against Blake Hall takes place.
There are lots of bosses here. There is a Rhyperior (which cannot be found after capture), Magmortar, Gallade, Dusknoir and Darkrai (which can only be captured again if the player talks to the Drowsy Guy on the top level).
After Team Dim Sun disbands Altru Tower, it is renamed Peace Tower or the Tower of Peace (Japanese: へいわのタワー Peace Tower) and opens to the general public. If the player returns to its top, the Drowsy Guy can allow them to replay the final battle against Darkrai.
In the Special Mission, Liberate the Tower!, Team Dim Sun's remnants reform under Kincaid's leadership to form Team Debonairs and retake control of the upper floors of the Tower, with the top floor of the Altru Building sealed off by vigilant employees. With Darkrai's help—who stayed behind at the Tower to protect the Luminous Crystal—the player must get rid of Kincaid's followers and capture his Drapion and Gliscor to clear the mission.