My first thought was to wonder how the carved figures were holding up the weight above. Upon research, I discovered they are in fact made of terracotta, constructed in sections around cast-iron columns. The history of this cathedral-proportioned church is recorded at stpancraschurch.org/the-building/history
To my sensitivities there is something about crypts that I find unappealing. It's used for art exhibitions now. I rather prefer art to be illuminated by sunlight.
It is all a bit strange how things change in this way.

Crypts have fallen out of fashion. I couldn’t find one on Airbnb.

...darkness forever...

“ Light's all very well, brothers, but it's not easy to live with.”— Mikhail Zoshchenko