Considering the category includes bunkers, crypts and scary government installations, it's not surprising subterranean buildings often have a slightly unsavory reputation. If it's something you want seen, logic dictates you don't place it at the bottom of a hole. That explains why the recently demoed Lowline concept, a proposed underground park inside an abandoned Manhattan trolley stop, has generated so much attention. The plan to redirect sunlight and create a lush green space under Manhattan literally flips our conceptions of utilizing underground space. But it's far from the only example of imaginative designs for subterranean structures. Here is a study of creative examples that show the potential of underground architecture beyond basements, bunkers and standard train hubs.