The Biggest Dome Ever Built (Paris)

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If huge spaces freak you out (looking at you, agoraphobes), look away now. Singapore's huge new stadium, SportsHub, just clinched the title for the largest free-spanning dome structure ever built—stretching more than 1,010 feet across at its widest point.

Designed by Arup, AECOM, and DPArchitects, this sprawling development doesn't just include a 55,000-seat stadium—there's also a network of pedestrian and cycling trails, infrastructure to hold all manner of games from cricket to rugby, a pool and a water park, a skate park, volleyball courts, space for canoeing and kayaking, a mall, and a huge rock climbing wall. And more. In short, it's its own city devoted to sports.

So, what about this dome? Well, it's a retractable roof that spans 1,017 feet at its widest point, and it can convert from one mode to another in only 48 hours. "Economy of means is a key characteristic of the main dome structure itself which uses one-third of the steel weight per square meter when compared to other large span structures of this scale," the architects told ArchDaily, explaining that the stadium is unusually efficient, regardless of its size. Hopefully Qatar and Tokyo are taking notes. [ArchDaily; Images via DP Architects]