The famed firm of Burnham and Root built the Rookery – named for the site's previous building, a temporary city hall that was popular with roosting pigeons – in 1888; Frank Lloyd Wright remodeled the two-story lobby atrium 19 years later. It's renowned for its contrast in styles: though it may look hulking and fortress-like 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 Trust outpost/shop in the lobby. Next door is a small gift shop that sells a variety of Wright–themed books, housewares and jewelry.