Directions rom CDG to Paris Nord to London St. Pancras

For directions to Gare du Nord from the airport, go to parisbytrain.com. Since you will need euros to get in to Paris, yes, get some at an ATM at CDG. Your hotel is in, actually in, St. Pancras station, hence the name Marriot St. Pancras. On the underground, take the Northern Line from King's Cross/St. Pancras to Elephant & Castle. Ask your Marriot hotel for a map of the Underground and of London.

Paris: RER B runs from the airport to Nord, no changes. London: a. The Marriott is a five-minute walk from the St Pancras International platform. b. The Northern Line runs from Kings Cross/St Pancras to Elephant and Castle, no changes. You'd almost have to get euro at the airport since you'll need them to buy the RER ticket.

Websites that will help you navigate from CdG to Gare du Nord: www.paristbytrain.com http://www.aeroportsdeparis.fr/ADP/en-GB/Passagers/Home/ http://www.ratp.fr/en/ On the commuter train which runs into Paris, watch the destinations board on the platform to catch an express train which will make fewer stops. This particular train has a reputation for thievery, mostly overblown, but keep your luggagge together and your wallets etc. carefully controlled.
Tickets for the train are sold by machine but most US credit cards don't work. Use your new euros with a ticket an agent.

Another thought...check with your bank to "buy" some euros from them before you leave the USA. Here is the map from the Marriott website. Looks like the other poster was right. Seems to be connected to the train station.
http://www.marriott.com/hotels/maps/travel/lonpr-st-pancras-renaissance-london-hotel/

Another thought...check with your bank to "buy" some euros from them before you leave the USA. Which will effectively double the price of the ticket.

Just a quick note that the Kings Cross station is on the next block from St. Pancras. It's even connected by a tunnel under the street. Very easy to get to. Since you will be at St. Pancras overnight, the British Library is on the other side of St. Pancras. It's free. The first floor and special bookroom is spectacular. The Magna Carta is in one of the rooms. The second floor has a wonderful cafeteria.

Tena, I've noticed that each time you ask about this trip you put a question mark after the station name Elephant and Castle. Why is that? Is it because you are uncomfortable with it, or because you don't like the name, or you don't think that it is the best destination. You haven't told us where, near E&C, it is. Is it walking distance, or will you expect to get a taxi? If you will need a taxi, you might consider taking the taxi the whole way from St Pancras. It will mean finding a taxi driver who is willing to go "South of the River". I'm pretty sure I've already mentioned this to you, but in case I haven't, make sure you are checked in at Gare du Nord a good 30 minutes prior to departure time or you won't go - strictly enforced.

Re Elephant and Castle: I read a long time ago that the name was a corruption of "Infanta de Castile" which was a lovely and amusing corruption. But then (damn google!) I found the name refers to a famous old inn & pub, the Elephant & Castle.