At more than 3 million square feet, this is the largest federal building in Washington, and the only structure for use by both government and private entities. A blend of classical and modern architecture, it is also officially the World Trade Center, Washington, D.C. The Reagan Building hosts special events throughout the year, in addition to its permanent art collection including a section of the Berlin Wall. You'll also be able to see the plans for the Dwight D. Eisenhower Memorial (slated for completion in 2016); as well as the Make it in America and Woodrow Wilson Presidential Memorial exhibits. Free guided tours are offered Monday, Wednesday, and Friday at 11. There's a food court on the lower level, and a theatrical group, the Capitol Steps, performs satirical works in the Amphitheater on weekends. In summer, check out Live!, a free concert series, performed daily from noon to 1:30. A farmers' market takes over the plaza on Friday during the spring and summer.