In reply to GDes:
https://www.climbsouthwest.com/events/dartmoor-in-a-day/
I think this is the first year of the event.
There used to be an annual walk from Cornwood (nr Ivybridge) to Okehampton. This was the O.A.T.S (Okehampton Adventure Training Scheme walk. It was used by lots of groups as training for the Ten Tors event. 28.5 miles by a more direct route via Hexoworthy and Postbridge. The section to Hexworthy was wet and tussocky but from Postbridge to Okehampton was much easier.
The route suggested for the ultra takes in some great running on some good surfaces. The sections South of Princetown largely uses the Abbots Way before getting onto the old tramway. The Northern section is very well established and solid underfoot.