You will start in one of the two blue boxes on the sides. Use a rocket launcher to tunnel down. Take about two shots in the back, then down about two to three shots. After that, just shoot out the walls in front (that the windows on the blue gate objects are) until you see light. Peek out and you can see the level below your box. Note: You may die a few times before accomplishing this.

In multi-player mode, select the Blasted Canyon level. When the game starts, look out onto the field and turn right at the wall. Get a rocket launcher and begin blasting the wall. Soon it will be large enough for you too fit in. Get inside, look down, and shoot a rocket (killing yourself). When you go back in, you should be under the floor. Begin blasting out some of the rock under the floor (killing yourself in the process.) After awhile you will have a cave under the floor. If you wish to make a sniper point, blast (under the floor) towards the field. You will soon see light, in which case you should blast open more until you can see the field. Note: Always bring a rocket launcher down with you, in the event you get stuck there is no getting out.