Artist Tomas Saraceno has asked visitors at his exhibition to rid themselves of any sharp objects - and you can see why. His Cloud Cities installation, currently on display at the Hamburger Bahnof Museum in Berlin, Germany, consists of large transparent spheres that lend themselves to an overall molecular aesthetic. Suspended in the air, visitors can walk inside the spheres as they tentatively balance in the midst. Tread with caution...no high heels allowed.