Charles River Esplanade

Charles River loops from the Esplanade Boston's classic is less a single route than a choice of loops: pick two bridges over the Charles and run out on one bank, back on the other, with Boston on one side and Cambridge on the other. The loop between the Harvard Bridge and the Longfellow Bridge, about 2.8 miles, is the easy first outing. Longer days are simple to build because every bridge is a turnaround; a long run from the Museum of Science bridge upriver is about 17 miles. Expect plenty of other runners, which is reassuring early and late.