The setting for this story was inspired by a trip to the Wieliczka Salt Mine, near Krakow, though the physical details of the mine got a bit forgotten as other aspects of the story (like the mud wrestling!) developed.

Here are some images of the mine (taken from the web because my photographs didn't come out).

...

The tunnels, caked with salt:

The cathedral:

Some of the relief carvings:

A display showing how mediaeval miners dealt with the build-up of dangerous gases (which collected in pockets beneath the ceiling) by igniting them:

Some of the 'horse gear', used to lift salt to the surface:

An underground lake:

A view of the gift shops and concession stands: