New St Michael’s Cave was discovered during tunnelling operations in 1942. Access was gained from the lower adit of the known St Michael’s Cave. The first sign was when their tunnelling appeared to create no rubble as it had fallen through the newly created opening into this previously undiscovered cave which may have remained sealed for some 20,000 years.
It is a karstic solution cave which occupies a rift inside the Rock. The cave's chambers include examples of almost all known cave formations, including a lake nearly 40 yards (37 m) long containing an estimated 45,000 imperial gallons (200,000 l) of crystal-clear water. This spectacular cave system is currently accessible to the public only with a guide by prior appointment.
There are no archaeological remains from New St Michael’s Cave which had been sealed, and therefore inaccessible to humans, until its discovery.