Sightseeing vacations are easy on the wallet because many of the activities are free. Washington, D.C., for example, offers a host of museums, monuments, and government history -- all for free. While lodging isn't cheap, there are ways to save money on transportation. Washington is easily walkable, and for destinations further afield, the regional mass transit system, the Metro, offers an unlimited day pass for $14.50. Boston is another city packed full of history and free entertainment. Take a walk on the Freedom Trail, which includes famous historical landmarks such as the sites of the Boston Massacre and Boston Tea Party. You can also score free tours of the U.S. Custom House and the USS Constitution, the world's oldest commissioned warship.