Great Falls is really pretty. The fee for the whole car is very doable and allows you to come back for 2 more days. There are 3 overlooks and lots of BBQ stations. I love this location. You'll get to see lots of mansions on your way to the falls and once there you'll forget that you're just 15 minutes outside of DC. Someday I'll figure out how to get to the MD side with the rope bridge...