A sprawling museum built across the old Charles River dam at the edge of Beacon Hill — the building itself is part Cambridge and part Boston. Inside are about 700 hands-on exhibits: a model of the human body big enough to walk through, a full-size T. rex skeleton, a model T model engine that's been running for decades, and demonstrations of static electricity using the world's largest air-insulated Van de Graaff generator.
The Hayden Planetarium has a 57-foot dome and hosts evening laser-and-music shows. The Mugar Omni Theater shows IMAX features on a five-storey dome. The Charles Hayden Theater of Electricity hosts the daily lightning show — million-volt sparks crash across the room while a brave staff member sits unaffected inside a Faraday cage.
Plan a full day if you have kids. Sundays in the school term are quieter; school holidays are chaos. Take the Green Line E branch to Science Park station, which deposits you at the front door.