Sure, there's always Fenway Park, the Freedom Trail and those zany duck boat tours. Part interactive museum, clubhouse and retail outlet, RunBase opened last spring near the finish line of the iconic Boston Marathon. Unleash your inner Cousteau beneath the new reflective ceiling dome, which gives the entire aquarium a shimmering undersea vibe. Ditto a leisurely walk through Boston Common and the adjacent Boston Public Garden, the heart and lungs of the city. A raucous alternative is a splashy ride on a duck boat: a World War II-style amphibious vehicle that rumbles past most of those landmarks. Other must-sees: the highly interactive John F.