Fort Reno is just a short bus ride away from my neighborhood. If you don't know anything about the history of DC, the designer was asked to include defensive forts and circles for artillery emplacements around the city, in case of attack. When the British attacked the city during the war of 1812, these plans were not quite up to the task. Now, the forts are great places to have free concerts while the circles are just traffic hazards. On Mondays and Thursdays during the summer, Fort Reno has free concerts providing that our weather holds clear.
Here's the schedule. DC also has Screen on the Green during the summer but sadly, no Mai Fest with mugs of Maibock.