How do you find the crevise in Metal Gear Solid 3

To get to Bolshaya Past Crevice in Metal Gear Solid 3: Snake Eater, head through Bolshaya Past South and Base to the north. Once you are at the Base, the exit is at the very top of the map. You can also destroy the parked helicopter, and it will be replaced by flying platforms when you get to Krasnogorje Mountainside later on.