My trip to UK

I'll be going to united kingdom next spring, it's my first time there it should be a lot of fun! I'm not really familiar with what's good or not there, can you guys give me some tips? I heard that the train ride on the north york railway is a whole lot of fun. It's apparently a train ride through beautiful country side, as you guys know I'm a nature, mountains, etc lover, so I'll be checking it out for sure. What other not-to-miss attractions are there to see?