River Thames Frost Fairs
en.wikipedia.org
en.wikipedia.org
[1] https://www.juliafullerton-batten.com/projectmenu.php?catNo=...
https://www.bbc.co.uk/news/uk-scotland-highlands-islands-258...
Edit: I spend a lot of time the Scottish mountains and I'm fascinated by glaciation so deeply disappointed that I missed them by such a relatively short period of time.
Or perhaps it it one of those things where it dropped out of though for sometimes decades at a time, but the Thames was such a large presence in their lives that when it froze over stories from parents/grandparents came flooding back and they wanted to recreate and have their memory of standing in the middle of it?
ETA: turns out it was the same one both times, the last Thames frost fair ever, in 1814.