Oasis 21 is the glass-and-steel canopy over Sakae bus terminal, designed by local architect Toshiyuki Komatsu and completed in 2002. The signature element is the Spaceship Aqua roof — a 60 by 30 metre glass pool suspended fourteen metres above ground level, with a thin film of water flowing across the surface. A walkway at the roof's edge lets you walk under the water, looking up through it to the sky.
Below the canopy is a sunken plaza ringed by cafes, a Pokemon Centre and event space, with subway, Higashiyama line and bus connections fanning out into the underground. The whole structure is illuminated at night in shifting colours. Worth a half-hour stop on any walk around Sakae.