I would like to call the city of Washington DC Memorial City simply due to the fact that there are numerous number of memorials built for the people who have made some difference to America. My long-standing desire to visit all these memorials came true during this visit and I did not miss this opportunity. We visited Lincoln Memorial, Jefferson Memorial, Korean War Memorial, Vietnam War Memorial, Washington Monument, JFK Memorial, and the newly built World War II Memorial. In the due course, I learned a lot about American history.
There is a lift ride offered at the Washington Monument, which takes you to 500 ft high in the monument. You get a very good view of the city from up there.
We got tickets to take the Capitol tour and also saw the most famous building in the USA: the White House. The Mall is an important landmark in DC with about 15 national museums. We were able to visit the National Air and Space Museum and Bureau of Engraving and Printing and actually saw dollars being printed.
Regarding tickets for all the above-mentioned places: the entrances for all the memorials, museums, etc. are free. But for some of them, you need to pick up tickets given at the respective places on first-come-first-served basis. These are limited tickets and can disappear quickly as early as before noon.
The tickets for lift ride in Washington Monument are distributed at the ranger station outside the monument. You can pick up the tickets and come back later at the mentioned time to take the tour. For people who have exact plans of their trip, they could purchase the tickets on internet by paying $1.50 per ticket. The free tickets for a trip to see the dollars getting printed at Bureau of Engraving and Printing are distributed at the building. The free tickets for Capitol tour are very limited and are distributed at the kiosk located on the Capitol grounds. Or you could request for a tour through your congressman 2-3 months in advance. The same is the case for the White House tour.
One more important thing is that Washington DC is very beautiful in the night too. All the brightly lit monuments are worth a visit after dark.
One could take any of the several privately operated tours in DC like Tourmobile, Old Town Trolley tour, DC Ducks tour, etc.