The aquarium has some after 5pm deals on Friday nights. You should call to find out because they are not on their website. I want to say one time we got in for $5 after 5. You don't get as long to walk around, but the school/camp tours are long gone by then. They have a new jelly fish exhibit that we loved! There were things we'd never seen before. IMO, the dolphin show has really gone down in quality and the 4D theater creeped my 8 year old out. The back of the seat stabs you when there's an alligator on screen. We didn't like the extra stuff, but loved the aquarium in general.
Try to do a drive by of Charm City Cakes if you can. We love Duff on Ace of Cakes! You can't go in, but we got some cute pics outside. You can get t-shirts with the logo at the inner harbor tourist traps.
Have fun!