in one corner of my backyard i am digging a hole. i've been working on it for some time now and it's pretty deep. i'd say like thirty feet or so with a four foot diameter (that's a two foot radius).
one day it will be very deep. if i were to write up a list of hobbies, digging holes would be one of them.
i have no plans for said hole. but having a really deep hole in one's back yard always sounds like a good idea. so much you can do with one.