Athletes will be taking part in the Ultra Tour run which winds itself around Edinburgh and the Pentland Hills.
The race began at 7.30am this morning and will last until around 5.30pm this evening with the first finisher expected to finish at the Commonwealth Pool at around 12.30pm.
No roads are closed for the event but with such a long distance, drivers and pedestrians should expect to come across the runners throughout the day.
Runners will then head towards Craigmillar Castle before heading up Blackford Hill.
That won't be where the uphill struggle finishes though, with a trip through the Pentland Hills greeting them before they begin their return to the city.
After descending from the hills they will travel through Colinton, Slateford, Stenhouse and past Murrayfield before heading north towards Newhaven and Leith docks.
Athletes will have the choice of stopping at three 'Pit Stops' along the route at Swanston Golf Club, Saughton Sports Complex and Dock Place in Leith.
There runners can stock up on water, food and take a trip to the toilet if needs be.