When I lived in London, I had friends who thought nothing of skipping over to Paris, Brussels, Calais or Amsterdam for a lunch date, returning the same day. And this was before the Chunnel, when you had to travel by air or by boat. I even indulged in this myself a couple of times, though I regarded the journeys as excessive extravagances. But it makes sense if you are in Britain for a while and think you might not have a chance soon to visit France. You can now just pop over for the day, thanks to the British rail system.
BritRail's package allows you to experience the novelty of the high-tech Eurostar train through the Chunnel (31 miles, 20 minutes), and gives you a free pass valid on Paris' extensive public transport network (the metro, buses and the RER suburban system) as well as a map of The City of Light. Standard-class adult prices for these excursions are actually $20 LESS than a one-way full fare Eurostar ticket ($199). Standard-class excursion fare is $179 for adults ($164 for child 4 to 11), while first-class (which includes free food and beverages on board) is $279 for adults ($264 for a child).
You leave Waterloo International Terminal at 7:23 AM, arriving in Paris just three hours later. You then have 6 and a-half hours before you have to depart Paris' Gare du Nord at 8:07 PM, again taking just three hours to reach the other end. Departures are on Monday through Saturday in April, May and October, on the same days plus Sundays from June through September.
The excursion is available only from BritRail, so call them soon at 877/677-1066, as space is limited. Ask for the "Day Out to Paris" tickets.