When I am in DC, I always stay at Kathleen's house. It's a perfect location for research and/or tourism purposes. The metro Eastern Market is near. All cafes, restaurants, CVS are at mere at 10 minutes by walk. The neighborhood is beautiful (especially during the Cherry blossom season), welcoming and quiet.
The house is clean, cozy, beautifully decorated. There are a lot of books and photographs everywhere. In the rooms you have everything you need for short or long staying (a microwave, a fridge, a coffee machine, dishes, cups, spoons, knives etc). The bathroom is very clean and you can use some shampoo, shower gel and soap. You can wash your clothes by using Kathleen's washing machine and dryer.
When you stay at Kathleen's, you are at home, or even better.
It's important to mention that Kathleen is always vey helpful and kind. She can give you a perfect advice what to see in the city, where to eat, what to do for fun. She cares about people. It's always a pleasure to talk to such an intelligent and interesting person.
Very highly recommended!