This white marble obelisk is 555 feet tall and recognizable around the world. Get a ticket on the grounds and it's free to tour it. I have visited the Washington Monument since I was in grade school and not much has changed except that the admissions are timed now (a group every 15 minutes) and that the upper inside marble walls are covered in plexiglas. That does not detract from the experience from the viewing portals over Washington DC and beyond and the interesting elevator rides with commentary up and down. I think that there's no better view of the Capitol City than from the four vantage points atop the viewing deck. It is also interesting to see all of the other world famous monuments and museums by walking around. The building history and materials requisitions, also fascinating. The LIncoln and Korean War Memorials are directly across from the reflecting pool so be sure to see them also. The Jefferson Memorial is not a far walk from there and Tidal Basin are on the other side of Monument hill.