To go from Dover to Paris, there are a few options (and nuances) to keep in mind.
1. Take the EuroStar from St Pancras station in London to Paris. The direct EuroStar takes just over 2 hours to reach Paris. To get to London St Pancras first, take the high-speed Southeastern train from Dover Priory. This train uses the EuroStar tracks and is the fastest way (~1 hour) to reach London from Dover.
Instead of London St Pancras, you could take the EuroStar in Ashford (25-minute train ride from Dover) - though only one or two trains operate this route on a given day.
Summary: Dover Cruise Terminal >>> Taxi to Dover Priory Station >>> Southeastern train to London St Pancras station >>> EuroStar train to Paris Gare du Nord (or
Disneyland Paris)
2. Take the ferry from Dover to Calais (or Dunkirk) in France. It's a 90-minute crossing, and there's a sailing pretty much every hour. From Calais port, you can take a cab to the Calais-Frethun station for a high-speed TGV train (1.5 hours) to Paris Gare du Nord. Alternatively, you can take the Eurolines bus straight from Calais port to Paris - though the travel time will be roughly 4 hours.
Summary: Dover Cruise Terminal >>> Taxi to Dover Ferry Terminal >>> P&O Ferry to Calais >>> Taxi to Calais-Frethun station >>> TGV train to Paris Gare du Nord (>>> RER train to Disneyland Paris)
3. Drive. For rental cars, bear in mind that not all companies allow driving outside of the UK. Plus, you will be driving on the other side of the road. If you do drive, you will take the Eurotunnel shuttle at Folkestone (near Dover). You basically drive your car on to the shuttle train in Folkestone (UK) and drive off it 35 minutes later in Calais (France).
Alternatively, you can take the ferry to Calais from Dover and then rent a car in Calais. A caveat: the Magic typically is in port in Dover on Sundays, and hardly any car rental office is open on Sundays in either Dover or Calais.
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My recommendation? If you want the fastest option (outside of flying), go with #
1. For the cheapest, do #
2 with the Eurolines bus. For the most flexible, rent a car somewhere as in #
3.