Kettering.
first from my great Gran's window that had a view of the MML with peaks hauling coaches.
then when i started secondary school in 1982 i would go down to the station at lunch times.
there were often trains on test from Derby running in between the morning and evening rush and there was still a signal box then but mostly HSTs by then and if you stayed long enough you saw the same few in both directions.
school holidays meant day trips on my own to all the London terminus to watch 50s, 86s, 87s etc
and visits to Grandparents in the New Forest where i'd take the train to Eastleigh and Salisbury, Westbury and even Exeter on my own for the day.