3D printers have been around for a while. They're often used when prototyping consumer products -- you can feed a CAD file (a computer rendering) into the 3D printer and it creates an object (usually made of plastic) that you can feel and fiddle around with. This is handy, because it helps you get an idea of the the "real world" size of an object -- and usually a small object at that. But Italian inventor Encrico Dini has created a printer called D-Shape that uses sand to create very large objects. Like buildings.
A PhysOrg article about D-Shape says this:
The completed material resembles marble, is stronger than concrete, and does not need iron reinforcing. The printing process can successfully create internal curves, partitions, ducting, and hollow columns. Dini also has lunar plans for the D-shape, and is in discussions with La Scuola Normale Superiore, Norman Foster (a UK architecture firm), and Alta Space, as part of the Aurora program run by the European Space Agency (ESA), to build a modified D-Shape that could use lunar regolith (moon dust) to build a moon base. Dini will carry out trials in a vacuum chamber at Alta Space's facility in Pisa to ensure the process is possible in a low-atmosphere environment such as the moon. Dini said his ultimate dream is to complete Guidi's Sagrada Familia in Barcelona, which has been under construction since 1882 and which is not expected to be completed until 2026 at the earliest.
Here's a video of the device in action (warning: in Italian, and with a strange intro, but interesting nonetheless):