Tourists outside St Chapelle cathedral

Like Versailles or the Eiffel Tower or the Louvre Museum, plan on spending time in a line waiting to get in. Due to stricter security procedures, expect to pass through a metal detector and your bags will be checked too. So bring plenty of material to read or an iPod to listen to music. It also helps to have your own drinking water and a snack. The other tip I can give is to use the restroom before you line up and to figure out the nearest rest-room in case the wait is too long. Paris is very good with public toilets on streets, though, lines can be long sometimes and they may not be clean. So it is best to use those inside restaurants and other public buildings.