A truly grand theater with historic landmark status, the Auditorium gives visitors a taste of late-19th-century Chicago opulence. Designed and built in 1889 by Louis Sullivan and Dankmar Adler, the 4,000-seat Auditorium was a wonder of the world: The heaviest (110,000 tons) and most massive modern edifice on earth, the most fireproof building ever constructed, and the tallest building in Chicago. It was also the first large-scale building to be lit by electricity, and its theater was the first in the country to install air-conditioning. Originally the home of the Chicago Opera Company, Sullivan and Adler’s masterpiece is defined by powerful arches lit by thousands of bulbs and features Sullivan’s trademark ornamentation—in this case, elaborate golden stenciling and gold plaster medallions. It’s equally renowned for otherworldly acoustics and unobstructed sightlines.

During World War II, the building sheltered GIs, and its theater stage was turned into a bowling alley. The theater reopened in 1967 following a $3-million renovation made possible through the fundraising efforts of the nonprofit Auditorium Theatre Council. Remnants of the building’s halcyon days remain in the Michigan Avenue lobby, with its faux-marble ornamental columns, molded ceilings, mosaic floors, and Mexican onyx walls.

Because it’s still a working theater and resident home to the Joffrey Ballet, it’s not usually open to the public during the day; to make sure you’ll get in, book a guided tour ($12). Get tickets online or purchase them beginning 30 minutes prior to the tour at the Auditorium Theatre Box Office. (To schedule a group tour for 10 or more, call tel. 312/341-2300.)

An insider tip: If you can’t get in for a tour, you can still get a glimpse of the building’s historic past. Around the corner on Michigan Avenue, walk in the entrance that now houses Roosevelt University, and you’ll get a sense of the building’s grand public spaces. Take the elevator to the school’s 10th-floor library reading room to see the theater’s original dining room, with a barrel-vaulted ceiling and marvelous views of Grant Park. Allow 1 hour for the guided tour.