There are approximately 5,000 know examples of hut circles on Dartmoor. which range from barely visible walls to easily identifiable structures. The best examples, some of which are late nineteenth century restorations, are at Grimspound - see:

http://www.legendarydartmoor.co.uk/round_house.htm

http://www.legendarydartmoor.co.uk/grim_pound.htm