I recently walked the Thames Path, a nearly 200-mile walking trail along the River Thames. These are some of the questions I asked, and can now answer. I wrote a separate post detailing all of my Thames Path accommodations, including what I paid. What is the Thames Path? If you’ve ever been to London, you’ve probably seen signs for it along the river. The Thames Path is a British National Trail that runs along the River Thames, all the way from the Thames Barrier in far eastern London to the source of the river — quite literally a spot on the ground in the middle of a field, near the village of Kemble. The Thames Path is about 184 miles.