A simple bat box. Certainly it's cheaper to make one out of plywood, but it sure is easy to just run it on the printer. Full disclosure: I have no idea how bats will respond to a 3d printed bat box. And I'm sure you could optimize the print settings on this, particularly where there are overhangs, to use less material. This was just a quick and easy Saturday project with the kid, and figured I'd share it in case it can help others make a cozy home for their favorite eaters of mosquitos.