Altering cave is a special dungeon that ordinarly houses an infinite amount of Zubat however this can be changed using the special E Reader device and the proper E Reader pokemon cards will modify pokemon into the dungeon therefore instead of finding Zubat you can find Smeargle for example and so on.
Zubat.
Inside icefall cave.
Nothing but Zubat.
Inside the Cerulean Cave. HMs Required: Surf
You can nly get inside it after beating the game and inside it at the end you can catch Mewtwo.
you have to beat the elite four. and, you have to rescue Lorelei on four island. And inside the cave lies... MEWTWO!
inside cerulean cave near cerulean city.
Firered don't have a "solar cave"
in firered and leafgreen, after u beat the elite four, go to cerulean cave. mewtwo is inside.
use cut. read up on your braille.
In there you can only find zubat but the reason why its called the altering cave is because you can change what appears inside using a E reader device and E reader cards.
mewtwo is in mystery cave :D