"[Arc de Triomphe was] commissioned in 1806 by Napoleon, shortly after his victory at Austerlitz, it was not finished until 1836. There are four huge relief sculptures at the bases of the four pillars... Engraved around the top of the Arch are the names of major victories won during the Revolutionary and Napoleonic periods. The names of less important victories, as well as those of 558 generals, are to found on the inside walls. Generals whose names are underlined died in action. Beneath the Arch is the Tomb of the Unknown Soldier, and eternal flame commemorating the dead of the two world wars."
This photo was submitted in 2008 by Mr. K. He writes: "...I was in Paris for 4 days...went all over and to the Arc de Triomphe and was surprised to see, 1.) that you could go inside/on top of it, and 2.) that it has a restroom inside"
If you examine these photos carefully it becomes apparent that they feature the same men's room corner. However, it appears that the urinal has been upgraded in the intervening years.