MCAD had lots of great little exhibits located on the historic Old Post Office Building! They also have tours every other Saturday that go throughout downtown Miami. The tour guides are genuinely interested in what they are talking about, and you will learn everything you could possibly want to know about the historic old buildings in downtown. If you can fit the 2 hour walking tour into your schedule (20 minute orientation inside) you should definitely do it. You also don't have to worry about getting too hot because you are continuously going in and out of buildings (air-conditioned) even in the heat of summer (I went in July; 95 degrees)!