Downtown on a weekend afternoon can be pretty quiet, unless there's some sort of festival/parade. The ToonSeum is a perfect place to visit if you're in the area and have got some time on your hands. (We had extra time before a Heinz Hall performance.)
I'm not too well versed in cartoons (other than ones I grew up with) and didn't know about the strip that's their current special exhibit, Brenda Starr, but everything about the museum was still fascinating. I especially enjoyed the desk of the Walt Disney animator, at which you're welcome to sit down and draw. There was also a Daffy Duck cartoon playing on a projector, for a nice touch of nostalgia.
The guy at the front desk gave us a very warm welcome and a helpful, brief explanation of the exhibits. The place is small, and it'll take you less than an hour to look around, but it's great to have a place like this downtown.