Relic Castle (Japanese: 古代の城Ancient Castle) is a large castle and the ruins of an ancient city that is over 2,500 years old, located in the middle of Desert Resort. It is made up of several floors and a maze. A Volcarona appears at the end of the maze, and can be caught after the player has defeated Ghetsis and Team Plasma at N's Castle in Black and White, or after obtaining the Quake Badge, via entrance from the Relic Passage, in Black 2 and White 2.
The Relic Castle is the ruins of a city built by one of the twin heroes and his corresponding dragon and are said to have been the heart of a civilization for people and Pokémon in the Unova region. The civilization dates back to at least 2,500 years ago, at which point it was at its peak.
The Relic Castle, although accessible early in the game, cannot be fully explored until after entering the Hall of Fame. Five floors deep, only the first and second floors can initially be entered: a Worker explains that the lower floors are covered in sand and are impassable until he has cleaned up a bit.
The first floor is hazardous, with two patches of quicksand which may suck passersby into the second chamber. A nearby scientist explains that if players walk over the middle of the quicksand, or run anywhere near it, they will fall through the floor. However, walking slowly anywhere besides the middle of the quicksand is safe. Behind the furthest patch of quicksand is a Backpacker who has found two rare Fossils. To relieve her load, she offers the player one of her Fossils, and notes that one of Lenora's colleagues knows how to revive the Fossil into an extinct Pokémon.
After N has awakened ZekromB/ReshiramW at Dragonspiral Tower, the next few floors have been cleared up, allowing the player to venture deeper into the castle, which, at this point, is filled with Team Plasma Grunts. At the lowest reachable floor, the player will encounter Alder and Ghetsis, with the latter giving a brief speech before leaving.
After completing the game, a new entrance will open up on the bottom floor of the castle. The player will enter a complex maze and chase a Team Plasma Grunt, who must be fought to continue through the maze. After defeating the Grunt, he will explain that he was lookout for a sage who was experimenting. The player can find one of the Seven Sages, Ryoku, towards the southern part of the maze. He explains that he wants the Pokémon that lives in Relic Castle to impress Ghetsis. After he is taken away by Looker, the player can continue to the shrine of Volcarona and battle it. After continuing west through the maze, the player can travel up some stairs to the other exit of Relic Castle, where TM26 (Earthquake) is found.
In Black 2 and White 2, most of the Relic Castle has become filled with sand and is inaccessible, leaving only the first two floors (which are still accessible via the Desert Resort), and a portion of the lowest floor—including Volcarona's room—which is accessible via the Relic Passage.
Relic Castle appeared in The Adventure, where both Red and his Pikachu were seen entering the castle. Inside the castle, Pikachu accidentally stepped into a sand pit, causing it to fall down into Volcarona's room. Pikachu battled Volcarona and managed to defeat it, but was then suddenly confronted by a Landorus, which attacked.