Behemoth

Behemoth is the dimension where Reptaliths are from, and it has no other inhabitants.

Terrain
Behemoth is an ocean of magma a quadrillion light-years in diameter. The magma contains varying amounts of every natural element ad mixes at random, and if solidified it would form a pitchblende of different minerals. The temperature is 3,870 degrees Centigrade and the pressure is 80,000 atm, which results in huge spurts of magma whenever a Dimensional Rift is opened. Semisolid lumps occasionally form but always melt away.

Life
Behemoth has only one native life form, the Reptalith. These creatures are ageless, all but impossible to kill or even harm and breed extremely rapidly, but the population is kept in control by their pilgrimages to other dimensions.