Spent the afternoon at the MIT Museum. The bottom floor has different kiosks about current research projects happening at MIT. The second (MUCH bigger) floor is quite large and houses many neat exhibits, such as kinetic sculptures, holograms, a hadron collider photo gallery, and everyday household inventions.
All-in-all a neat place to visit, we finished it in 3.5 hrs. Admission is $10 per adult, but if you show a Charlie Card / Ticket, you can get a 2-for-1 deal.