What is so special about the combination of trains and walking?
The simple answer is - a lot!
The most obvious benefit is that travelling by train allows you to take linear walks, rather than having to do circular ones. If you use a car, your options are immediately limited to finishing at the same location where you started - unless you want to do some complicated arrangement with taxis, or relying on someone to pick you up. Sure, it means that you are limited to walks that start and finish at stations, but fortunately there are loads of those - as this site demonstrates.
There are other advantages too.
Using trains makes it easy to plan for groups of people to join you - you just need to agree train to meet on and that’s it (no issues with planning on where to pick people up or who goes in which car!).
And walking by public transport is very environmentally friendly. That is clearly true in a global sense - the CO2 emissions are close to zero if you are travelling at the weekends (or travelling in the opposite direction to commuters). But it is also true in terms of the local impact. Consider driving to a beauty spot to begin a walk. Firstly they have to tarmac over some of the beauty spot to provide somewhere to park. Then there are the fumes you emit driving to the park. In addition there is the noise from the traffic.
Walking by rail is a real no-brainer!