Barrier in London. Officially 184 miles (294km) in length (although the actual distance you walk will depend on a number of decisions you make en route), the path meanders, accompanied by its watery muse, through pristine and tranquil countryside, past historic sites and buildings, via pub, lock, weir, and the occasional scattering of waterfowl, to a city, once the fulcrum of an empire, and now the heart of modern day England. The river, responsible...