My grandfather was a railway worker on the Metropolitan Line back in the 1950s and I only just got him to talk about something that happened at Broad Street Station in June 1952. He was doing maintenance work on the tunnels late shift when he and a colleague heard what sounded like a train arriving - full whistles, mechanical sounds, the works.
Here's the problem: there were no trains scheduled. They went to investigate and apparently saw the ghost of an old Victorian steam locomotive pulling into the platform. Proper detailed - they could see it was an older model, colours and everything. It just... sat there for maybe thirty seconds, then vanished.
His mate saw it too, but they never reported it officially because they reckoned they'd be sacked for being drunk or mad. My grandfather has never been a drinker and he's the most straightforward bloke I know. He seemed genuinely shaken telling me about it after seventy years.