Didcot Railway Centre, Oxfordshire.

This is more of a static museum site, and there is a lot to look at. On the long, roughly triangular site are an engine shed and various displays, and three short train ride tracks, one of them being 7ft broad gauge. There are also stalls and a refreshment room. I recall that on my last visit after two or three hours I’d had enough of being on my feet and went to refuel in the café, while my train fanatic friend continued poking around the engine shed for another half hour. The admission charge includes everything, including train rides on steaming days. A modern railway runs alongside the site, so one can from time to time see a 21st century train swish past an early 20th century train pushed by a tank engine.
The site adjoins Didcot Station, so if you feel that arriving by car to look at old trains is a bit silly, you can arrive by train from the north, east, or west.