Chloe Parkman
BBC News, South West
Thousands of people will descend upon Dartmoor at the weekend to take part in the 63rd Ten Tors challenge.
The annual event, between 9 and 11 May, is usually attempted by 2,400 teenagers in 400 teams of six, and organisers said routes ranged between 35 and 55 miles (56 to 88km).
The challenge, organised by the British Army's Headquarters South West, involves teams navigating routes across the northern half of Dartmoor in under two days.
"Teams must be self-sufficient, carrying all they need to complete their route and stay out overnight safely," organisers said.