I don't do much camping in the sense of using a tent to sleep in, but I'm a big fan of bothies. In case you don't know what a bothy is, it's a basic building in a remote location that is left open and is free to use by anyone, for rest and overnight stays. They tend to be REALLY off the beaten track, and they're basic in the sense that there's no mains services, and often no toilet, and you need to take in everything you need yourself (sleeping bag, food etc). Hiking to one and staying in it for a couple of nights is an often unpredictable but usually very rewarding experience.
There's about a hundred or so of them in the UK, mainly in remote parts of Scotland, maintained mostly by the Mountain Bothies Association, but there's also a few in the north of England and north Wales.
I've had some brilliant adventures in them, and would love to hear stories of anyone else who has used them.