Not hidden, because it’s in plain sight and on many lists, but Planet Word museum doesn’t get enough hype. It’s great if you’ve grown tired of the Smithsonians.

A few trails I like run through Dumbarton Oaks Park, as well as the trails between Glover Park and Foxhall Crescent.

If you like to look at gorgeous houses, walk the Kalorama neighborhood.

Edit: Planet, not plant.