(NOTE: This is re-purposed from an old post to celebrate out upcoming DC trip.)
The 9-11 Memorial at the Pentagon is open 24/7 which makes dusk an interesting time for a visit.
Regrettably, the last lines of Witold Rybczynski's Slate piece on the memorial rang very true. Some of trees are already failing and a few light bulbs were temporarily out. Hopefully these can be addressed, because this is an important memorial at an important place. Reading reviews like this and then visiting the place in person is an important design experience for students. The Fall Field Trip is a great time to try it - just take the Metro to the Pentagon stop.