Quake Arcane Dimensions 1.8 - Arcane Adamantine (Evil 100%)

This level on the surface appears to be a normal watery pipe level, but if you break all of those things on the walls you open up the techbase side of the map. Then the entire place gets repopulated with tech monsters and you have to go throughout the whole thing again to get all the kills. An interesting idea to lengthen play time I think.