Also quite nice are the atlases published by SPV https://www.spv.co.uk/atlases.shtml - they're available for many locations and show historical and live rail lines.

Once you know where a rail line was you can often still "see" them on satellite maps - even if the rail was pulled up decades ago (as it still will affect property lines, etc).

Also see: https://www.railstotrails.org/ - many rail lines have been converted to trails.