Downtown, Penn Quarter, and Chinatown are a tale of three cities. Washington, D.C.'s Downtown is staid, compact, and home to some wonderful hotels, though pretty quiet at night. Chinatown and the Penn Quarter jump at night with their many shops, bars, and restaurants.
The Capital One Arena sits in the middle, and the nights are supercharged when the Capitals or Wizards are in town. There are also many great museums and theaters, including Ford's and the Warner.