"It's a Melter crypt. Melters are—I don't know what they are. You heard your friend on the comm. The attackers he was talking about, they have to be Melters. They... just come out of the walls. Or up from the ground. Anywhere there's meltmassif. If they touch you it's like a stun blast. Then they carry you to a crypt and stick you into the rock."
Aeona Cantor[src]

Melter crypts were underground caves situated on the planet Mindor that were formed from the rock meltmassif and used by the Melters, an energy-based sentient species. Within the caves, the Melters imprisoned inside the meltmassif captured individuals that they had encountered on the surface of the world. The Melters considered the treatment of their captives to be "pest control," because solid-state sentient beings sometimes fired stun bolts at the Melters, and the energy-based beings failed to understand that their actions could cause harm to their captives. During the Galactic Civil War, Mindor served as a stronghold of the Imperial warlord Shadowspawn, and numerous Imperial shadow stormtroopers, native Mindorese and New Republic personnel were imprisoned inside the Melter crypts, where most of the captives starved to death.