Sonambutron

The Sonambutron was a machine constructed by the Nauians fearing that their world, Pollux V was threatened by meteor showers and an ensuing ice age. They retreated in sleeping chambers in suspended animation.

The sonambutron was under a landmass later known as Mount Idyll; it was powered by the planet's geothermal energy and equipped by a defensive mechanism: androids would fend off intruders by telepathically assuming their deepest fear.

The machine was programmed to re-activate again in the next solar eclipse, however they would not predict that in the meantime the planet's moon would be destroyed.

For the remaining millennia they remained in slumber until an away team of the USS Enterprise (NCC-1701) with Captain James T. Kirk, Spock, Dr. Leonard McCoy and Ensign Everts arrived on the planet to investigate. They discovered the doorway into the sleeping complex and managed to reactivate the machinery.