Russian Railways have recently introduced an upgraded overnight service direct between Paris and Moscow, called the Trans-European Express. The trains on this route reach speeds up up to 200km/hr as they travel through five different countries en route.
The train carries a range of Luxury, First and Second Class carriages, as well as a restaurant car. The sleeping compartments are configured as either 3-berths, 2-berths or single berths. You can opt to share a multiple berth compartment with a stranger, if you would rather not pay the extra for a single berth. Each compartment doubles up as a sitting room during the day time, with beds that fold down for the evening. Each room has its own basin, and towels, linens and toiletries are provided.
The train's Luxury carriage offers four compartments, arranged as single or twin compartments with private bathroom facilities, as well as telveision system and complimentary breakfast.
A dining car is attached for the length of the journey, although it is Polish between Paris and Warsaw, and Russian between Brest and Moscow. Each carriage also has a samovar, which provides hot water for drinks and snacks.
If this route doesn't take your fancy, there are alternative ways of reaching Moscow from Western Europe, including journeys from Cologne, Brussels, Helsinki and even Amsterdam.