hole^4

Working off of https://www.shapeways.com/model/723930/desk-toy-hole-thru-a-hole-in-a-hole.html by denali3, this goes one further, adding yet another "hole through." Not sure it's really an improvement, though, partly because at that point, where do you stop? Also, denali3's is all "inside" its sphere: if it were filled with something, these tubes would really be holes. Mine you have to imagine the filling mounded up a little, so as to give a bigger viewing window.

Still, frosted detail is totally the way to go with either: it's transparent, and the support material melts out of even most deeply-nested holes.