Just came across this walking event, not an ultrarunning race but still a great experience.
"The TGO Challenge is an annual self-supported walking event across the Highlands of Scotland, west coast to east coast. It started in 1980 and was the brainchild of the well-known writer and mountaineer, Hamish Brown. The Challenge is held every May and is sponsored by TGO, the walkers’ magazine, in partnership with Rab, the outdoor equipment specialist, and the adventure trekking company Himalayan Kingdoms."
Participants are given 15 days to complete the journey.