Location from pokemon-adventures-rgb by
A treacherous cave system north of Cerulean City where Mewtwo retreated after its rampage — one of the most dangerous locations in Kanto.
Cerulean Cave is where Mewtwo hid after escaping Team Rocket and rampaging through Cerulean City. The cave is naturally dangerous — filled with high-level wild Pokémon — but Mewtwo's presence made it exponentially worse. Its psychic emanations affected the local Pokémon, making them more aggressive and powerful. Red and Blaine entered the cave together to confront Mewtwo, leading to one of the arc's most intense battles. The confined space of the cave made Mewtwo's psychic attacks even more devastating — there was nowhere to dodge, nowhere to hide. Red's capture of Mewtwo with the Master Ball ended the threat, but the cave remains one of Kanto's most dangerous locations.
A deep, dark cave system with winding passages, underground rivers, and an oppressive psychic aura that intensifies the deeper you go. The strongest wild Pokémon in Kanto inhabit these caves, drawn by the residual psychic energy. Mewtwo's chamber at the deepest point pulses with visible psychic distortion.
Also known as: Cerulean Cave, the Unknown Dungeon