The Cheesecake Factory cheer:
The Baltimore Aquarium is fantastic. There is a dolphin show and an open aerie-type area with bats, sloths, tropical birds, and tarantulas.
Get this, we went on a Monday evening, and we were basically the only people there. We got the royal (presidential?) treatment. We had two tour guides personally attending to us and showing us all the cool things at the aquarium. They even tried to wake up the sloth for us. (No dice, he's nocturnal.)