The Toronto SkyDome, Canada

The Toronto SkyDome is the world's first major league, multi-purpose stadium featuring a fully retractable rigid-steel roof to serve as a fully open air stadium in good weather and a heated or air-conditioned indoor facility in variable weather. It has a capacity of 54,000 seat designed as a multi-purpose sports and entertainment complex. The retractable roof employs a unique system of three moveable roof panels with two modes of movement, resulting in a compact nesting of roof panels in the open position, exposing 91% of the seats to the open sky without casting shadows on either the seats or field. The roof opens in 20 minutes in winds of up to 65 km/h and has successfully opened and closed over 200 times since completion of its construction.