Metro is working on tracks this weekend, so beware if you are taking the Green, Yellow or Red lines.
DCist has the full list, but starting at 10 pm tonight, the Green line won't be running between Fort Totten and Greenbelt, there's a shuttle bus instead. In addition, the Yellow line stops at Mt. Vernon Square the Red line is single tracking with a lot fewer trains than usual. Then on Monday, everything will be on a Sunday schedule.
Not too much fun.