Blueprint Magazine describes a very neat machine:

In a small shed on an industrial park near Pisa is a machine that can print buildings. The machine itself looks like a prototype for the automotive industry. Four columns independently support a frame with a single armature on it. Driven by CAD software installed on a dust-covered computer terminal, the armature moves just millimetres above a pile of sand, expressing a magnesium-based solution from hundreds of nozzles on its lower side. It makes four passes. The layer dries and Enrico Dini recalibrates the armature frame. The system deposits the sand and then inorganic binding ink. The exercise is repeated. The millennia-long process of laying down sedimentary rock is accelerated into a day. A building emerges. This machine could be used to construct anything. Dini wants to build a cathedral with it. Or houses on the moon.

What do you think, readers? What would you build with a giant 3D printer that lays down sticky sand?