This is absolutely fascinating! I'm so impressed with the manager who was happy to show you the cellar. The history is intriguing and I am sure there are stories but you'd probably have to do some digging to find them.

You might even find that they were used to move important people around (high ranking clergy possibly) without them travelling on the surface and being in public.

Cannabis isn't far fetched either, I can totally believe that and I doubt anyone would be willing to corroborate it though.

What a marvellous find. Thanks for sharing!