Highest Hills and Mountain Railways

I'm currently planning some of the bigger trips for 50 at 50 and visiting the Isle of Man is on my list, not least because they've got lots of little railways. Including one up Snaefell it turns out.

I was already planning to go up the mountain railway on Snowdon so two potential side plans emerge:

1. Try to go up all the mountain railways in the UK (there's not a lot, the one up Cairngorm being the other obvious one).
2. Go up the tallest peaks in each of the countries in the UK. This does mean climbing Ben Nevis mind you, which is not trivial, especially as you start from pretty close to sea level. Scafell Pike is no picnic either at 3,209ft although at least you can start that one from about 250ft up.

Food for thought anyway. I shall mull it over.