[arkhitektor]

I've never been there, so I can't speak to how comfortable it is inside on a hot day, but it apparantly has no air conditioning.

Dedicated in 1980, the 10,000-window Crystal Cathedral seats 2,800 worshipers and its marble chancel accommodates up to 1,000 musicians. Years ahead of its time in conservation design, the Cathedral employs no air-conditioning, relying instead upon natural air currents which come via staggered rows of louvered windows, controlled thermostatically. Also part of this cooling system are two dramatic 90-foot-tall doors which open at the right of the chancel - a feature carried over from the Neutra sanctuary.

http://www.crystalcathedral.org/about/history.php