I am watching Retsupurae's Mortal Kombat Mythologies video where Sub-Zero is going through the four elemental temples. None of the ideas are particularly inspired but why not steal the easy stuff too.
1. Water temple could be completely underwater (lake or ocean bed) or it could just be a sewer level.
2. Fire temple has metal rooms that grow increasingly hot. Early rooms could have metal ceilings, then walls, and finally floors. The ceilings and walls cause fatigue (and damage if you got too close to the walls) while the floors would damage and sear characters due to the direct contact and heat convection.