If you are presenting a play or film that takes place in a cave, working in the real thing may not be practical. You can instead bring the cave to you by making a fake cave wall. This wall can be attached to a temporary frame, or stapled directly to a real wall if one is available. All of the materials that you need for this cave wall are available at your local hardware store.
Making a Frame
Cut two 3-foot lengths of 2-by-4 board for each sheet of plywood used. If you are building a wall inside an existing structure, skip to the next section.
Screw two boards to the bottom of each sheet of plywood, extending out from the rear, with 3-inch wood screws. Screw through the front of the plywood and into the end of the 2-by-4 piece.
Place the frames next to each other, creating an unbroken wall.
Connect the frames with scraps of 2-by-4 board, positioned across the seam between sheets of plywood and screwed in place. The frames do not need to be held in place any more securely than this, you simply want to prevent them from separating if bumped.
Place sandbags on the legs to prevent the frames from tipping over. Their weight will hold the frames in place.
Building the Wall
Bend wire mesh into the shape of the desired cave wall. You can use a large sheet from a roll, or several small pieces with the ends twisted together.
Staple the mesh to the frame or wall with a heavy-duty staple gun. It will form the under structure for the cave wall.
Spread a tarp on the ground under the wire mesh.
Put on a pair of rubber gloves and a respirator.
Hold a spray can of expanding insulation foam 2 to 3 feet from the mesh surface. Spray the foam into the mesh. It will break up as it sprays, covering the mesh in an irregular pattern.
Allow the foam to expand and harden into a rocklike texture.
Paint the wall with gray or brown latex paint. Allow it to dry.
Hot-glue items such as plant roots and moss to the wall to make it appear to be underground, if desired.