The obvious Boston is a 2.5-mile marked walking route through the colonial city; the less obvious one is two of the best art collections in the United States, a working ballpark and a ferry out to the harbour islands.
The Freedom Trail
A 2.5-mile line of red brick and paint linking 16 historic sites from Boston Common to the USS Constitution. Following it yourself costs nothing; the Freedom Trail Foundation's costumed guided tours are ticketed, and several of the individual sites charge their own admission.
Isabella Stewart Gardner Museum
25 Evans Way, a Venetian-style courtyard house left exactly as its collector arranged it, including the empty frames from the 1990 theft. Admission is free every Thursday evening; popular entry slots sell out, so book ahead.
Museum of Fine Arts
465 Huntington Avenue, a ten-minute walk from the Gardner, with a very large collection across Egyptian, Asian and American art. Look for the 5 USD Third Thursdays evening rate and periodic free-admission days rather than paying full price.
Fenway Park tours
Hour-long public tours run 9am to 5pm April to October and 10am to 5pm in the off-season, at 30 USD adults and 21 USD for ages 3 to 12. On game days the last public tour is three hours before first pitch. Book online up to 180 days ahead; phone 617 226 6660.
Boston Harbor Islands
A national and state park of 34 islands and peninsulas reached by seasonal public ferry, with Georges Island and its Civil War fort and Spectacle Island the two main stops, plus Peddocks. Ferries run in season only and get cancelled for weather, so check the schedule the same day.