This site is probably known to die-hard UK rail enthusiasts, but just in case, I'll post the link here:
https://railwaymap.org/?fbclid=IwAR3unf4CrdnmMb-12D5yMJS8VIikS53LC0fVdwCN3KPntaNe0EG6R5pXSRU# (https://railwaymap.org/?fbclid=IwAR3unf4CrdnmMb-12D5yMJS8VIikS53LC0fVdwCN3KPntaNe0EG6R5pXSRU#)
"RailwayMap is a newly started project to provide a way of looking at the railway as it existed at any given point in time from the first wagonways in the Northeast in the early 1800s to now."
I can't find an option to choose a timeframe yet, but it's early days.
Is this a current map or does it show historical lines well? But still, you can see how much the UK relies on it's railways even today, more so then here in the States.
Did you know https://www.openrailwaymap.org/ ?
That's railway all over the world! But without a historical history.
Great, I didn't know of these. My favourite is
https://railmaponline.com/
Where the lines are helpfully colour-coded to help you understand which companies controlled each line, and includes narrow-gauge lines, plateways, and even city tramways.
I honestly like Google Earth. There is an option to overlay rail and subway lines on the globe and you can show things like stations as well.