Instant walls of sand
Magnus Larsson has proposed building an ingenious structure in the Sahara Desert: a 6,000 km-long wall of sandstone made by flushing bacillus pasteurii through loose sand. The bacteria quickly solidifies the sand, thereby providing a wall to stop the advance of the desert or even structures for people to live in.
I researched different types of construction methods involving pile systems and realised that injection piles could probably be used to get the bacteria down into the sand -- a procedure that would be analogous to using an oversized 3D printer, solidifying parts of the dune as needed. The piles would be pushed through the dune surface and a first layer of bacteria spread out, solidifying an initial surface within the dune. They would then be pulled up, creating almost any conceivable (structurally sound) surface along their way, with the loose sand acting as a jig before being excavated to create the necessary voids.
This sounds more like sculpting or baking than architecture.