Check out a couple of sketches for the new stadium...think bobsled runs in the winter, and mountain bike runs in the summer, and think of the world's largest green roof... a sunken stadium, with a massive green roof, which serves as a public park in downtowm Minneapolis. The slope of the roof can be used as a bike, ski , or bobsled run . See public places such as Millenium Park in Chicago, Central Park in NY, http://j-drawingaday.blogspot.com/2012/06/day-244-drawing-minnesota-vikings.html#!/2012/06/day-244-drawing-minnesota-vikings.html