Looking for vacation activity in a major city that could serve as a "second-wind generator" for my 9-year-olds.

Hello,Last year, my family spent a day in Niagara Falls (Canada-side). It was exhausting, walking in such heat, but we made it to the giant SkyWheel, and the half-hour spent there (air-conditioned, slow mover, beautiful vistas) served as a wonderful "second-wind" generator, and the kids had enough energy to pursue the itinerary for the rest of the day.This year we are going to Boston; and I suspect that for the limited time that we will spend there, there is entirely too much for them to do. Instead of cutting a program out or two, I was thinking of finding an activity they can do sandwiched between two big activities, that can also help provide for them that necessary second-wind.Any ideas? (Or should I bite the bullet and cut out an activity)? via /r/Parenting http://ift.tt/29cmrQT