Speculation

Hints that will be more relevant later:

Sacrifice victims

Children to fire.
Women to water.
Men to the blackest evil (earth+air).

4 Elements for the elemental evil:

Earth West Altar, Brown robes
Air Central Altar, Ivory robes
Fire High Altar, Scarlet robes
Water East Altar, moss green robes

Warning on the altar

THE POWER OF ELEMENTAL DEATH
BRINGS MORTALS LOW
BUT RAISES THE NAMELESS ONE HIGH

Mosaic on floor by altar

Speculation

Temple of Elemental Evil DougBecker