Paris...So what a fun day you'll have with X number of hours before & after your fabulous lunch & before the Eurostar return to London. By the way, that's what you're taking, the Eurostar that goes thru the Chunnel. I would shop for something very special to remind me of a fabulous day trip to Paris, not cologne or perfume since it doesn't last. You should buy something you'll always have. I have a daily reminder of one of our trips to Paris, bought a piece of jewelry at Galleries Lafayette after attending a fashion show there & remember if you go there to look at the beautiful ceiling ! The store on Haussman. I had 500 Francs that I'd won at a trade show, bought a Lalique pendant that is a beautiful blue, probably had to augment with some USD. Something from Hermes' perhaps ? No, a piece of jewelry ! Enjoy, let us know what you do in the few hours you have.