/r/Ass is a subreddit devoted to the enjoyment, appreciation and sharing of booties. The site's description puts it perfectly: 'this subreddit is for natural and artistic images of female bottoms'. The site seems to focus more on amateur material and less of the porn-based approach to ass worship. It also has a tight policy on penetration and gaping, these guys ain't interested in any of that. If you want to share some bottom photography, you better damn well make sure it's fancy!
The site currently has 172,000 subscribers, making it one of the most popular adult-based subreddits that the site has. All of the images are also hosted on Imgur, so you can really navigate through the entire collection of material there in order to see what's up for grabs.
I've always been a big lover of reddit and use it daily: sadly, I wasn't subscribed to /r/Ass before today. The good news is that I've fixed my issue and now I'm off to enjoy some hot booty babes - I suggest you do the same!