/r/Porn is your basic subreddit when it comes to X-rated action - the premise is simple: share lots of porn. It should be noted from the get go that there are no real focuses in terms of content here - just so long as it features people having sex in some way, that's all that matters. The subreddit does have some strict rules for submissions however, and that includes a cross-post only schedule, no video links and no requests for sources. While a little restrictive, it still presents a decent way to ensure the integrity of the content without sacrificing your ability to share.
The subreddit currently has 45,000 readers and receives new submissions about once every day - a very slow rate, but to be honest, I think that's because it isn't really focused on any material in particular. One of the main points of Reddit is that any weird desire you could want fulfilled is there, and /r/Porn is the Jack of all trades but a master of none.