The Prada Transformer is a huge four-sided open-air building whose floor can be any one of its radically different sides. Massive cranes rotate it into place, leaving the other three to compose its ever-changing ceiling.
This isn't some neat concept, it's an actual construction, penned by Rem Koolhaas and the Office for Metropolitan Architecture, and built by Prada with help from LG and Hyundai Motor. It's framed out of steel and covered entirely with a "smooth elastic membrane" and it will be situated in Seoul, Korea, where it will be used for concerts, fashion shows and other cultural events.
I think the best illustration of it is this piece from Freshness Mag, when the Transformer was only in the planning stage:
As you can see, the hexagonal side is flat, and the square has some bleachers, so it works for "cinema" mode. The circular side has a giant cylindrical platform in the middle of it, which houses a projector when it's in the air for cinema mode, but then is used as a performance stage when it's flat on the ground in "special event" mode.
Shot from the air and as yet unpainted, it doesn't look like much, and reminds me less of the robotic Transformers of the 1980s than it does of the Dungeons & Dragons dice from roughly the same epoch. The question is, how in hell do you make sure that the thing is on level ground? And while we're talking, who has to hose all the mud off of it when it gets rotated to a new position? And most importantly, who gets to drive the crane? Ooh ooh, me me! [Dezeen]