Comment by ErroneousBosh

> But they also had some clay from deep beneath Vienna that they got from (iirc) some new metro digging

U5 Matzleinsdorferplatz, in der nahe Gudrunstrasse? I've been down in those tunnels for a visit, they're extremely cool. Unfortunately we weren't allowed to take any photos.

It's weird seeing what's going to be the bit where the platform is, when they fill the big hole in with concrete, and the sloping-up tunnel that'll be the stairs and escalator, but it's all just flat grey shotcrete. It's like looking at a clay render of it before the textures and bump maps go on ;-)