Start at the visitor centre at the base of Ben Nevis in Scotland. Once summited, run to Scafell Pike in England. Once summited, run to Snowdon in Wales. Once summited, the finish line is the Pen-Y-Pass car park at the base of Snowdon. The route can be run north to south, or south to north and route selection between the peaks is at your discretion. The total estimated distance is between 420 and 460 miles, this attempt was 455 miles.
https://www.threepeakschallenge.net/232292/running-on-empty
This attempt was to raise money for charity (The Royal Air Force Benevolent Fund and Tommy's, the baby charity) and increase awareness of the impact of baby loss on mental health. I believe it had been attempted 3 times before I did it, the previous fastest time that i'm aware of was around 11 days.
Link to social media for videos and photos:
https://www.instagram.com/toms_on_empty/
https://twitter.com/EmptyToms
virginmoneygiving.com/running-on-empty
https://www.strava.com/activities/2765399440
Link to news paper article: https://www.oxfordmail.co.uk/news/17938826.raf-pilot-run-450-miles-miscarriage-charity-tommys-raf-benevolent-fund/