It's not just the building, but possibly also what's underneath it... You folk from the other side of the pond might not realize, but Paris has over 200 miles of underground tunnels.. Partly used to empty the city's cemeteries, relocating the skeletons of the dead underground, so they co  7b7  uld release more land for buildings.. Partly used for smuggling, with exits out onto the Seine river.. During WW2 the Resistance made great use of them... a safer way to travel around in occupied Paris, rather than up on the streets, where they would have been asked for "papiren" (German is not my language..) Good article and photos of skulls floor to ceiling https://www.smithsonianmag.com/travel/paris-catacombs-180950160/