A truly grand theater with historic landmark status, the Auditorium is worth a visit to experience late-19th-century Chicago opulence. Designed and built in 1889 by Louis Sullivan and Dankmar Adler, the 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 electrically lighted, and its theater was the first in the country to install air-conditioning.

The 4,000-seat theater, which today is the scene for Broadway touring musicals, is a marvel of visionary design and engineering. 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 sight lines. In the days when the Auditorium was the leading theater of Chicago, the hydraulically operated stage could be lowered from view, creating a ballroom capable of accommodating 8,000 guests.

Owned since 1946 by Roosevelt University, the Auditorium has had a roller-coaster history. Originally the site of a 400-room luxury hotel and commercial office space, it fell on hard times during the Depression and closed in 1941. 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. Don't miss the lobby fronting Michigan Avenue, with its faux ornamental marble columns, molded ceilings, mosaic floors, and Mexican onyx walls. Another inside tip: Take the elevator to the school's 10th-floor library reading room and have a look at what was once the city's first top-floor dining room. Its palatial, barrel-vaulted ceiling, and marvelous views of Grant Park and the lake will make you want to brush up on your Dewey Decimal System.

The best way to see everything is to take a 1-hour guided tour, offered on Mondays between 10am and 4pm (call tel. 312/431-2354 to make reservations). Tours cost $6 for adults, $3 for seniors and students.

Allow a half-hour, one hour if you take the guided tour.