We both had different passes to get into the Paris Marathon, because I had been attached at a later date, and I was in a group that was ahead of him to leave first. He was in the final group.
Iain was carrying an injury at the time, so instead of running it he was going to walk it, with two plates attached front and back, dressed as one of the Teenage Mutant Ninja Turtles. We were able to get into the same early start so that the documentary looked good, and so that there were people around for many parts of the marathon.
Walking the marathon with a camera was hard enough. Because I wasn't running, I was just filming, people thought I was taking the proverbial and not really trying that hard. If I wasn't holding the camera, people just thought I was taking up a place.
Flying into Paris with almost no lead time, going directly from the train station to get camera equipment, arriving last minute. Finding and negotiating for the different production elements to get on the marathon, and getting the camera equipment necessary to film it.
Just me. Not a huge amount of budget.