Amazing story! Thank you for posting this, and bumping!
I wish this would have been known when I was in that part of Europe in the late 1980s.
From the article:
During World War II, a few locals with long memories used them as secret air raid shelters and then, once again, the caves were sealed. And that is how they remained until 1990 when Alain Jacques decided to investigate.
(edit)
Now, 18 years after Alain's first discovery, a £3 million visitor centre and a lift have been constructed. The Carriere Wellington, underground home of the Suffolk Regiment 91 years back, is, finally, open to the world.
It appears that the site has just been opened to the public and so there wouldn't have been anything for you to see at the time you were there.
Now, however, you have an opportunity to return and visit the area, and to do it in a time when it appears that the French are a bit more congenial toward us Yanks, which is an added bonus :-)