You have a wonderful husband! Being solo for a few hours is wonderful. Heck, I've found that being solo there for a day or two is great, too!
Especially as an at home parent, especially as a nursing mom with an exclusively nursed child, you know you probably don't get much of a chance to think about what you want to do. (not that other parents think of themselves exclusively! but with my old friends, the ones that worked (and this includes my husband, a very hands on parent when he's home) got to have what they wanted for lunch, sit around at breaks, etc...but I know from being at home that it's not always like that at home, LOL)
So anyway, just write up a list of things that YOU want to do. Snacks you might want to have and don't feel like having the family conversation "hubby do you mind waiting while I get in that massive line for *whatever snack he doesn't want to have at that moment*?" etc. If all you want to do is wander, then wander. If you want to take pictures of buildings, or the ducks, or whatever, just do that. IF you want to ride Screamin' 18 times in a row, do it. Whatever you want to do, do it.
I've since taken a one-night solo trip, a one day solo trip (at the end of a longer trip with some old friends), and I went on the ladies trip last weekend which is sort of like an en masse solo trip,LOL, but it all started with one rainy late afternoon at DCA, when it was cold and started raining and hubby and son refused to stay. So they went to the hotel and I had some glorious hours alone!