There are four Teaism shops in DC, we stopped at the one in the Penn Quarter, at 400 8th Street, NW (only two blocks from the International Spy Musuem or the Shakespeare Theatre.
The star here is tea, and they offer a variety of black, green, and white tea as well as tisanes (herbal teas) and Chai. They offer both a traditional and an Asian Afternoon tea and wonderful cookies, scones, and desserts, as well as some cold drinks and even cocktails. No coffee, though, this is a NO Starbucks' zone!
If you want to find a meal here, there are a number of interesting options. They have Japanese Bento Boxes (with several small dishes served in a sectioned box), Ochazuke, a Japanese rice and tea soup is available, as are a number of small dishes like soup and vegetable tempura.
Sandwiches inclue a very good portobello sandwich, and a couple others, and big dishes include curries (Thai, Indian, Japanese), an Udon dish, grilled duck, chinese noodle salad, and much more, including Ostrich burger. I like the variety of vegetarian options because I get to linger over the menu, but Mark, my husband, likes it because it is yummy.
Teaism Penn Quarter is near the Navy Memorial at the Archives/Navy Memorial stop on the green and yellow lines. It is also only about four blocks from the Gallery Place/Chinatown stop on the Red Line.