Cerulean Cave, also known as the Unknown Dungeon, is a location in the Pokémon video game series. It is situated near Cerulean City and is known for its challenging layout and strong wild Pokémon. Players can access the cave after defeating the Elite Four and obtaining the Surf ability. Inside Cerulean Cave, trainers can encounter various high-level Pokémon, including the elusive Mewtwo. The cave features multiple floors and hidden items, making it a popular spot for players seeking to strengthen their teams. However, navigating the cave can be tricky due to its complex design.