The famed firm of Burnham and Root built the Rookery in 1888 and Frank Lloyd Wright remodeled the atrium 19 years later. It's renowned because while it looks hulking and fortresslike outside, it’s light and airy inside. You can walk in and look around for free. Tours ($10 to $15) are available weekdays at 11am, noon and 1pm.
The walkabouts last 30 minutes, except on Monday and Wednesday when they run for 45 minutes and include access to the Burnham Library. It's best to reserve tickets in advance, but you can also walk up and purchase them at the Frank Lloyd Wright Preservation Trust outpost/shop in the lobby.
Oh, the building's name? It comes from the pigeons that used to roost here.