travel card(paris passe)

On all passes you need to do the math to see if it is worthwhile. I also bought the 6 day Paris Pass (without transportation) and saved significantly more than 5 euros but we were very busy. The pass helped skipping the line at Versailles but didn't run into lines anywhere else. On another visit I bought the 2 day pass and the only way it made financial sense was visiting Versailles and hitting all the smaller areas in the back. The longer your stay the easier it is to justify the Paris Pass. The carnet work well. You can buy these almost everywhere (except on a bus). Depending on your plans you can go through 2 to 6 per day. You can certainly share packages to avoid being stuck with too many at the end of the trip.

Purchase Eurostar tickets early to pay less.

I have no experience with the Paris Pass, but from other posts I've read on this site, it doesn't seem like the best deal. Each person in your group should buy one carnet (pack of 10) of tickets for the Metro and the buses. I was in Paris for 8 nights last fall and the carnet served me perfectly. You probably won't venture past Zone 2 in Paris, aside from going to Versailles (a different ticket) and to/from CDG (also a different ticket). The carnets or individual tickets should be enough. We bought our tickets to Versailles from a staffed booth at a Metro station booth. The Museum Pass is a good deal only if you visit enough sites for the pass to either break even or cost less than individual tickets to these sites. We each bought a 6-day pass that cost 69 euros. We added up the ticket prices of each place we wanted to visit and saved 5 euros with the pass. Also know that the Museum Pass allows you to skip ticket lines at places like the Louvre and Versailles, which can save you hours of time.

Given that a 2-day version of this pass costs $145, I'd say probably not a good deal. Instead consider a museum pass and carnets of metro tickets, and add the other stuff if you want. A hidden advantage of the museum pass: You'll end up visiting little museums of some interest because they are "free." If Belgium beckons do consider the amount of time you'd be spending on the train if you visit just for a day. There is plenty to see in Paris and London. But it is feasible.

For the Eurostar, it is really quite simple. Go to the official website - www.eurostar.com - and do it as soon as you can tie down your dates and times. Tickets go on sale either 120 or 90 days ahead (don't remember but it is easy for you to check) and the prices never go down. As time passes, the prices steadily rise. Unlike most trains, there is a proper check in process and security check before boarding and there is a strictly enforced minimum 30 minutes prior to departure check in requirement. Not waiting in the line 30 minutes before, but actually checked in. If you miss that, you don't go. So you need to be sure about your times.

I've been to Brussels and Bruge but not Ghent. From what I've seen, I wouldn't spend the time on a train to have a one day visit to either of them. Unless this is your umpteenth visit to Paris and London, I wouldn't take a day away from either of these cities for Brussels. I would only recommend visiting Bruge if it was on the way for a larger driving trip.

There is a Paris Pass, a Paris Museum Pass, and a Paris Visite Pass. They are three separate things, and yes, it is confusing. The Museum Pass is often a good deal, but you have to do the math to see for your itinerary. Here's the website: http://en.parismuseumpass.com/. No need to pay extra to buy it in advance. The other two are rarely good deals for most visitors. Remember that there are only 24 hours in a day, so a pass good for 60 attractions is not necessarily helpful; how many will you actually see? Yes, if your only trip outside of zones 1-2 is to Versailles and the airport (and for most people, that's the situation), don't buy travel for all zones. You'll do much better with either carnets of 10 tickets (shareable) or a pass just for zones 1-2 (if your 5 days fall in a Monday to Sunday stretch). For Versailles and the airport, just buy separate tickets (less than €10 each). Brussels gets strong polarized reactions. I'm in the negative group. Bruges is quite nice (to me - again, opinions differ), but I wouldn't spend the time and money to go there just for a day from Paris or London. Do follow Nigel's advice about the Eurostar and buy as soon as you can commit, or the tickets may be stratospherically priced and some runs can be sold out.

I like Brussels a lot but it's not good for a day trip, as the places worth seeing are dotted around the city and it would take up too much travel time.