Mark the boundaries of the cave you wish to create. Take careful note of any underground utilities that may be disrupted by excavation, such as underground power lines, water pipes, or sewage tunnels. Make sure that you will not be violating any local laws or municipal codes by excavating on your land, and obtain any required permits for the use of excavation equipment.
Begin to excavate the earth where the cave will be located. If your cave will have an entrance to the surface, digging should be done at an angle that will allow the placement of stairs or a ramp for easy access. Dig to the desired depth, taking care not to damage equipment on the bedrock layer which typically exists about 14 feet below the surface. Do not dig below the water table, if it is encountered.
Carefully lay any reinforcement structures into the cave, such as a concrete floor, and any cement or hardwood support structures that will be used to support the roof. Typical underground cave areas use concrete "shells" which can be laid into the cave area and act as a template for the area.
Replace a portion of the excavated earth on top of the cave's shaping structures, compacting the soil, yet taking care not to crush the structures. Fill the area above the structures until the earth is level with the area outside the cave's perimeter. Use a dump truck to remove any excess earth and plant grass seed on the newly-turned earth, if desired.
Enter the cave's interior and check for any possible sources of weakness, failing reinforcement structures, or a possible cave-in. Also check to be sure that the cave is properly ventilated to the outside air. Clean any excess dirt from the interior and finish the cave as desired, furnishing it with any necessary items.