Eiffel + Arc
Although the Eiffel Tower and Arc de Triomphe were not on our priority list, we found ourselves in the general neighborhood of Eiffel late in the afternoon on our first day. We bought some cheese and wine from a nearby shop, sat on the lawn and watched the crowds, then wandered across the Seine for a much better view of the tower and watched some breakdancers for a bit.
We realized the sun was setting soon and that would probably be a great time to head over to the Arc, which is at the crest of the Champs-Élysées. Although the war memorial is 200 years old, cleaning and restorations in recent years made the limestone seem golden in the evening light. It was an unplanned end to the day, and one of our favorite memories of Paris.