Some cracking arses on display in this thread ! A lot of pounded passages too by the look of it. Me, I like a bit of resistance to my thrusts, so neat tight holes would be number one with me. I get quite a turn on with bum curvature too, especially if there's a neat pair of balls swinging below the target !
Here's a few from my collection - ( might find a few caverns for you later ! )