Artist Aki Inomata's 3D-printed acrylic shells for the hermit crab. See the entire project at http://www.ifitshipitshere.com/hermit-crabs-don-3d-printed-cityscapes-shells-project-migration/ <<< omg tell me you're just joking.... Holy [not so holy word]
These are hermit crab pools. This isn't a DIY, but this article can give you some ideas. It is beautiful. I am going to be making a DIY for hermit crab pools soon on my blog, http://careforyourhermiebabies.blogspot.com/ but my crabitat is not yet ready for the pools. Hopefully it will be posted up on my blog by July 30th.