Think of the most uncomfortably hot, humid day you've ever experienced in Seattle and multiply that by 10 Maybe won't be so bad pre-June, though...
Since you are a veteran, Arlington National Cemetery (especially changing of the Guard ceremony) is a very moving experience; there are tram tours if you don't want to walk a lot:
The Vietnam Veterans Memorial brought me to tears more than once (I joined the Navy prior to the end of that war).
I volunteered at The National Zoo for five years, but haven't been back since 1994. All the places mentioned here so far are easy to look up online (websites such as I linked above, with times open, costs, highlights etc). Once you've narrowed down some choices, make Mr. Google your friend!
Think of the most uncomfortably hot, humid day you... (show quote)
This was my first stop. Arlington! Two mass gravesites. I walked everywhere. Eleven miles the first day. Eight and seven the next two.
Pat, on my trip back in May, I walked 11 miles the first day, 7 & 8 the next two. I was by myself so felt a little venerable at night so only shot daytime.