Legendary Beasts

Ok. I don't want to seem stupid, but where's the cave that the legendary beasts are waiting in and how do I get there? I've done it before, but I just can't remember.

I know that they all run in dif. directions, and you can catch the one that's opposite of your starter (will be roaming).

There is only ONE of them available, you can't get all three in one game
they appear on a random route roaming Kanto after you beat the elite 4

and as you already know they will appear depending on your starter pokémon

Raikou for Squirtle
Entei for Bulbasaur
and Suicune for Charmander

I though there was a cave that you had to go first to make one of them roam :S I'll check around and try to run into it.