We're going to be in Paris from September 21-25, so I've been trying to book tickets for a few key things we'd like to see and do. Multiple sites I tried like Sainte-Chapelle and the Arc de Triomphe showed no tickets available on the 21st or the 22nd. I have now discovered that is when European Heritage Days are taking place, so those monuments are open to the public for free hence there are no timed entry reservations available.
On the one hand this seems kind of cool since there will be special tours and events taking place all over the city for those days. On the other hand I was hoping to minimize the amount of time we spend standing in lines as much as possible, and I suspect that this event might mean very long lines. For example, there are free guided tours at the Arc de Triomphe all day on the 21st, but it doesn't look like they take reservations. Does anyone have any experience with European Heritage Days who can confirm if I am correct about the lines?