Where is the crevise in Metal Gear Solid 3

It's a few stages (when you enter a stage, the screen turns black and it displays it's name in English and Russian) past the ruined warehouse (where you first meet Sokalov, Ocelot, and Eva) and it's just past a stage that has a enemy stronghold and weapons storage house.
Immediately after the crevice is a cave. I hope it helps.