I recently built a couple of recessed bunker's in 2 enclosures for my box turtle and Russian tortoise. They were easy to build. I just dug a hole, placed 3 cinder blocks, back filled dirt, then placed a board on top. Maybe I will throw some dirt on top of the board to provide some insulation and possibly make it a bit cooler in the bunker. I live in Southern California and temperatures are crazy warm right now. We are having highs in the 90s in late winter. I'm so glad they have another cool spot to retreat to. They each have a small version of Tom's Night Box as well but they still get warm when the sun beats down on them for part of the day. Has anyone else built bunkers?