Charles River Reservation, Boston, Massachusetts This 20-mile reservation stretches along the Charles River and offers plenty of activities, from picnics and playgrounds to sports fields, boating, and bike paths. Over 20 miles of trails are available to bike, walk or run. The reservation features mostly easy to moderate trails with varied route options. Trails in this park range from easy hiking trails and are great for the whole family, with elevation gain ranging from 6 to 285 feet. The most popular trail is Charles River Pathway Short Loop with an average 4.7 star rating from 1,188 community reviews. Trail types vary frombeautiful riverside walks along the Charles River on a popular bike/pedestrian shared pathtoa 23.7-mile loop trail that is considered moderate. Key highlights includeviews of Boston and Cambridgeandpassing Massachusetts Institute of Technology’s campus and Harvard University. The trail features architecturally interesting bridges and passes the Watertown Yacht Club. The reservation is highly accessible, withpaved trail surfaces typically at least 4 feet wide and mostly gentle grades (5% or less).