Charles River Reservation stretches from Boston Harbor up the river for 20 miles. Recreational activities abound at this park. There are athletic fields for all your sporting needs, there are trails for runners and cyclists, there is a par course, a skating rink, a playground, tennis courts and a swimming pool. The reservation is a fantastic multi-use park.
From Boston: Take Storrow Drive West. Pass the Harvard Square exit and then get in the left lane. Bear left at the Rte. 2 interchange onto Soldier's Field Road, following the signs for Newton (do not cross the Eliot Bridge to Cambridge).<br /><br />For the bike trail: Access to path is plentiful throughout the city just head to the river. If you are driving in head to Back Bay if you can find a meter spot great. If not park at Boston Commons or one of the other garages. If you start in Back Bay there are several foot bridge to get you across Storrow Dr. just head north on Arlington, Dartmouth, Fairfield or Mass Ave till you hit the end and you will see on of the bridges.
http://www.tripleblaze.com/trail.php?c=3&i=1905