Lucca
I’ve never had an ‘obby. My bloke has had all the er..”sad” ones. Train spotting and stamp collecting and now bird photography ( not twitching… although he does that due to a medical condition ?
Nothing wrong with trainspotting! 
Articles about job hunting used to say, when filling in an application form, and it asks about hobbies "don't put stamp collecting!". I have often why that was often said.
You might like this story that I read many years ago about trainspotting. I think a man who, when young, had been the boy in the story, wrote about it in a magazine about steam locomotive preservation, about 1990.
I think the story probably happened some time in the 1950s.
At the time, express trains on the East Coast main line, London King's Cross to Edinburgh, were (often) hauled by a particular tpe of locomotive, a type A4. They are those very distinctive ones with the streamlined sloping front.
35 were built, but one was destroyed in the war, so 34 were running in the 1950s.
The boy in the story lived close by the track somewhere along the route, conveniently close enough to often be trainspotting as the trains passed by at speed.
He had seen 33 of them, so needed to see one particular one so as to have seen them all, each had a number and a nameplate.
So he wrote a letter, addressed to the Shedmaster of the Locomotive Department at King's Cross, and asked if that particular locomotive could be rostered onto some particular express on some particular day.
And on the day, it was.