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...you asked for stuff to see. Some of the places that nobody ever goes to (because they are relatively unknown), are the
National Arboretum, (over in NE,)
The Kenilworth Aquatic Gardens, (across the Anacostia, over in far SE), and by far my favorite of all the D.C. museums,
the Textile museum.
Thompson boat house and
Fletcher's, farther up river, are both places you can rent a canoe or rowboat and enjoy the river from a different perspective. It's a great place to be a museum tourist, because many of them are free admission.
I have spent many hours wandering around the grounds and collections of pre-Columbian stuff at
Dumbarton Oaks. The gardens themselves are a wonderfully designed national treasure.
And high on the list of obscure tourist attractions are the
catacombs under the old Franciscan monastery, also out in far NE, near the Maryland state line.