Challenger's Cave is a post-game location where you can battle trainers and catch a variety of Pokemon. You'll find some rare and powerful Pokemon, but no legendaries are present.
Here's where you can find the Legendary Pokemon in Pokemon Black:
* Victini: This Pokemon is not found in the wild. You can only obtain it by connecting with other players via the Global Terminal and accessing a special event.
* Cobalion, Terrakion, Virizion: These Pokemon are part of the Swords of Justice trio and are found in the Relic Castle after beating the game.
* Reshiram/Zekrom: The legendary Pokemon you chose at the beginning of the game will be encountered at the end of the main storyline.
* Kyurem: Found in the Dragonspiral Tower after beating the game, you can combine it with either Reshiram or Zekrom to create Black Kyurem or White Kyurem.
* Landorus, Tornadus, Thundurus: These Pokemon can be obtained through special events or trading.
* Cresselia: Found in the Dream World after beating the game.
* Mewtwo: Found in the Giant Chasm after beating the game.
* Keldeo: Found in the Giant Chasm after beating the game. You can only obtain its Resolute Form after completing a special event.
Remember that some Legendary Pokemon require special events or trading to be caught. Keep an eye out for announcements and updates from Nintendo or The Pokemon Company for more information.