a wild, open and hilly part of Devon in south-west England, 365 square miles/945 square kilometres in area. It is a national park and a popular place for walking and horse riding. Dartmoor ponies are small, dark brown horses with long hair that live wild on Dartmoor. Parts of Dartmoor are also used for military exercises. Dartmoor prison is a men's prison in the middle of Dartmoor, well known because it is difficult to escape from.