Arc de Triomphe 

  As we stayed in a hotel just blocks from the Arc, we got to see it quite a bit.  You'll note that as you look through the pictures, they change from day to night to day.  There were multiple photo shoots!  The views from the top are not as impressive as those from the Eiffel tower, obviously, but taking the tour is still interesting.  Inside the Arc is actually quite a bit of space.  It was interesting to find out the various uses of the Arc over time (although I can't, for the life of me, find documentation of that).  One of the most interesting activities relating to the Arc is trying to get a good front-on picture from the Champs-Elysees.  Fortunately there are pedestrian islands in the middle of the road both near the Arc and at the base of the hill.  Obviously, the Arc is a must see if you're in Paris, even if you don't go to the top.

Click here for pictures of the Arc de Triomphe