You can always count on Gray line tours. I did this tour on my visit to DC... This tour is so flexable. Takes you to all the major attractions in Dc and you are also able to hop on and get back on the buses if you decid you would like to stay and explore a certain momument. The people that sell the bus pases are so helpful as well. Gray line also offers night tours of the city but I was not able to do that part. I would suggest purchasing a two day pass that way you can take your time touring the city. If you don't like to walk to each site I would highly suggest Gray line tours. So the next city I visit if Gray line is avaible I would take advantage.
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