Hi Barney; I wouldn't say it's worth going all the way t Norfolk just to see that, we were on the way back from London when we visited. The mine which you enter is basically a hand-dug chalk pit which you can descend into via a ladder. At the bottom of which are galleries coming off in all directions, however these are all gated unfortunatly 😉
Whilst driving around Norfolk I noticed quite a lot of other sililar looking chalk pits, and wondered if they went underground, and if so what access was like, but unfortunatly I didn't gather much info on that...
I believe there's another ancient chalk mine in sussex, which I embarassingly didn't know about when I was once living there.
regards
Kein geneis kanaf - Cain gnais canaf
Byt vndyd mwyhaf - byth onddyth moyav
Lliaws a bwyllaf - Líows o boylav
Ac a bryderaf - ac o boryddarav
Kyfarchaf y veird byt - covarcav yr vairth
Pryt nam dyweid - poryth na'm dowaith
Py gynheil y byt - Pa gonail y byth
Na syrch yn eissywyt - na soroc yn eishoyth
Neur byt bei syrchei - nour byth bai sorochai