9000 KM
Ferry and/or train (Channel tunnel)
There is not any direct rail connection between Belfast and France. You will need to travel via London, using ferry service. It will cost you $90 to travel from Belfast to London (ferry and train both), and another $117 to travel to Paris from London via train.
You can't travel directly from Amsterdam to London by ferry because London doesn't have a ferry port. You would have to travel from Amsterdam to Hook of Holland by train (or drive), catch a ferry to Harwich and then take a train (or drive) to London.
Flying would be the quickest and easiest but if you want somthing different you can get a ferry to England and then travel in the underground train to Paris.
About 2.5 hours
A boat train is a travel service with a train timed to arrive at a ferry port in time for the onward travel by ferry.
Sort of; you can travel by rail from London to Salerno (in Italy). You can then get a ferry from Salerno to Limassol.
By train (Eurostar from London or Ashford to Calais, Lille or Paris); with your car on Eurotunnel (Folkestone to Calais); with the car or as a foot passenger on the ferry from Dover to Calais or Dunkerque, Portsmouth to le Havre, Cherbourg or Saint-Malo, and several other routes. The shortest ferry crossing is Dover-Calais. From Calais to Paris by autoroute takes about 2.5 hours. To get from Calais to Paris by train (other than Eurostar) you have to change at Boulogne sur Mer.
You can't travel directly from Gatwick to Paris by train. You will have to take a train to London St Pancras and then get on another train to Paris. Unbelievably, you can't fly from Gatwick Airport to Paris either.
The Eurostar travels between London and Paris, and between London and Brussels. It does not travel between Paris and Geneva.
No. London and Paris are both inland, and while both are connected by rivers to the sea, there are no ferries between the two cities. So you would first have to travel overland to one of the ferry ports in England and the to France and then by land to Paris. You can travel other ways, by air and by train through the Euro Tunnel.
A train journey from Moscow to London is possible but not directly. As London is on the British Isles, the only connector for trains is across the English Channel to Paris.