$5 or less: WalkingTown DC

Did you know there used to be a red-light district a stone's throw from the White House? How about that Georgetown was once a hotbed of spy activity? These are just a couple of the intriguing topics covered this weekend during the spring installment of WalkingTown DC. More than 100 free walking tours and 11 bike tours are on the menu this year, including old favorites -- "Before Harlem, There Was U Street" and a nighttime bicycle tour of the monuments -- and some additions, such as the aforementioned adults-only tour "Rowdies, Madams and Painted Women" and a bicycle tour of the eco-friendly solar-powered homes in upper Northwest. Although you can just show up for some of the excursions, others require a reservation, so head to the Cultural Tourism DC Web site to snag a spot before the tours fill up.

-- Stephanie Merry