Day trip to London from Paris

Rick's Paris guidebook has entire chapter on doing this trip efficiently. The underground lines from St Pancras/King Cross station will take anywhere you want in the city quickly. But since you're just going to there one day, the hop on/off tourist buses might be the best stress free option. As to what to see, flip through the pages of the London Top Ten guidebook:
http://tinyurl.com/klr9k9

What to see and do on a short visit depends upon what your personal interests are so you can give them the highest priority. For ideas, see the London day trip suggestions in the Rick Steves Paris guidebook.

I highly recommend that you plan to stay overnight in London, even if you have to pay for an empty hotel room in Paris. You won't feel nearly so rushed and you'll have time to go to the theatre or to a concert. London theatre is not to be missed!

Buy your Eurostar ticket now,, prices only go up,, not down.

I second the recommendation for leaving your hotel room in Paris empty for one night and staying over in London.

We did this in reverse.....were staying in London and took the chunnel train to Paris for an overnight trip with our teenage daughter. It was wonderful to see her expression the first time we saw the Eiffel Tower.

Thanks to everyone who posted a reply. We are looking forward to our trip!

Happy Travels,
Kris

We always fly into London, stay 3-4 nights then Eurostar to Paris on our 2-week trips. We avoid CDG at all costs. Buy the Eurostar tickets when they go on sale, 90 or maybe 120 days prior to your trip. If you have only one day to visit London, take the first Eurostar train out and the last one back.