Well, Boston is a tourist town. But if I have out-of-town guests, (and I have) I take them to the Union Oyster House. It is located right in the heart of "tourist land". The building itself is loaded with history. Originally, it was a stable with rooms upstairs for the stable hands. The downstairs booths were some of the original horse stalls. (pre G. Washington) The booth where JFK used to spend Sunday mornings reading all of the pile of newspapers has a marker on the wall. I prefer the upstairs rooms. You are never rushed. They save downstairs for the tourists and handicap. (Fast turnover.) The stairs (I swear) are the original ones. Very narrow and steep. They specialize in seafood, but you can find non-seafood dishes on the menu. Something for everyone.
Standing out on the sidewalk, you can watch the folks sitting at the oyster bar, down dozens of raw shellfish.
Looking up at the second floor, you can see the wavy glass in the windows. I don't know if those are the original window panes, but they are very old. It is one of the oldest (if not the oldest) continuing operating restaurants in the country. It is a tossup with the Warren Tavern in Charlestown. Another place loaded with history. It is said that this place is where some of the Sons of Liberty (Paul Revere, Sam Adams and other of that ilk.) would meet.