Getting the the Great Chamber requires a high-clearance 4WD vehicle to drive the long, sandy road. The parking area for the Great Chamber is located at Cutler Point on the map. There are a couple of ways to get there because there's a wide network of 4x4 roads in the area, but most people start from Johnson Canyon Road.
From the parking lot head up the east side of the rock formation as you climb a sandy trail towards a large rock alcove filled with sandy. The trail is fairly well-trafficked, so it's easy to follow. If you don't have the proper vehicle or 4x4 driving skills, guided tours are available.