Washington DC, Cherry Hill Park
We are just leaving DC and I want to recommend Cherry Hill Park for anyone coming to the city. It is expensive ($80), but worth it. They have tons if amenities, pools, hot, tub, cafe, mini golf, etc.
But as almost everyone is here to see the city, that is where it really shines. They have an orientation to teach you about the train and bus system that is really good.
The Metro bus actually stops in the park, connects to the train, and that will take you to anywhere in the city. It is so easy.