Here are some maps of long distance rail services in Europe (with a bias towards Paris). Some of the maps are very stylised and don’t reflect physical routes closely at all.
All maps are from 2018 and will not be updated - I made these as part of a separate and unfinished project and am publishing them here in case they are useful to anyone.
First up, Eurostar. London to Paris or Brussels in about 2 hours, Amsterdam in under 4 hours plus seasonal routes to the Alps in winter and South of France in summer and a separate service to Disneyland.
There is a sleeper service that connects London to Scotland and includes stops in some remote Scottish towns.
There are a number of options and operators. Domestically, the main high-speed, non-budget INOUI service connects Paris to most French cities while the budget OUIGO service connects Paris to a smaller selection of cities (mostly from non-central-Paris stations). There is also a sleeper service that is pared back virtually every year so use it while you can!
International operations are more fragmented. There are several operators connecting France to neighbouring countries.
DB-SNCF connects Paris, Lyon and Marseille to Western German cities including Frankfurt and Munich. Thalys connects France to Belgium, the Netherlands and Western Germany at high speed on modern trains. SNCF-Italy and Thello connect France to Northern Italy (by rather utilitarian sleepers in the case of Thello). TGV Lyria expensively connects Paris and Marseille to much of Switzerland and lastly, Renfe-SNCF connects Paris to Barcelona and Marseille to Madrid (slowly).
German ICE trains serve almost all of Germany and the main cities of Denmark, Netherlands, Belgium, France, Switzerland and Austria. Please note that the map below is particularly simplified and stylised.
Finally, Spain’s AVE network connects the main cities, mostly at high speed.