In 2009 we made a trip to the abandoned Coal Mine of Hasard de Cheratte (or: Cheratte 10) near Liège. While I took my pictures at the work bench, suddenly there was noise and excitement and many people – armed people as I could see from my hide-out.
Finally I got into a bunch of Paint Ball players – but anyway, I was scared for the moment and we had to interrupt our photo session at this lost place. Hasard de Cheratte is finally demolished since 2018.
You should take a look at its Wikipedia Page.