Consider it the Super Bowl for architecture buffs.
Open House Chicago returns this weekend to give visitors from around the globe the rare opportunity to step inside some of the city's most treasured landmarks typically closed from public view.
The now-annual event run by the Chicago Architecture Foundation (CAF) provides a city-wide history lesson spanning 18 neighborhoods and 150 structures, CAF officials told The Huffington Post.
This year, though, a handful of landmarks on the tour will open to guests for the first time in more than half a century. Among the most anticipated is the Allerton Hotel -- home to the iconic "Tip Top Tap" sign -- which has been closed since 1961.
The hotel's bar and ballroom once hosted stars of the day like Bing Crosby, Bob Hope, Frank Sinatra and Lucille Ball, according to ABC Chicago. The ballroom is the featured stop inside the Allerton, which was purchased by a French hotelier earlier this year and renamed the Warwick Allerton Hotel.
You'll also get a peak inside downtown's The Sky-Line Club, one of the oldest private membership facilities in town. Nestled in the Old Republic Building, it was constructed in part in Sussex, England before making its way to the Windy City.
Not every stop on this year's open house tour is steeped in history, however. Among the two featured stops for 2014 are the headquarters of two millennial-era e-commerce giants: daily deals site, Groupon, and popular t-shirt maker, Threadless.
OHC organizers say they hope the free event draws at least 60,000 visitors, up from last year's crowd of 55,000. In 2013, visitors from 71 different countries and all 50 states poured into the city to take a peek into the best-kept secrets in Chicago.
Open House Chicago runs Saturday, Oct. 18 and Sunday, Oct. 19. Free, no tickets are required.
"The Library" at 190 S Lasalle
Open House Chicago
According to the CAR:"This postmodern masterpiece pays homage to Burnham & Root's Masonic Temple and includes 'The Library' on the 40th floor with floor-to-ceiling windows and sweeping views of the city."
The Forum
Open House Chicago
Built in 1897, the onetime mainstay of the Bronzeville cultural scene -- the cultural and historical capital of Chicago's black population -- The Forum has what's possibly the oldest hardwood ballroom dance floor in Chicago.Hosting everything from Nat King Cole performances to political meetings, The Forum fell into disrepair and was nearly demolished in 2011. New owners, however, plan to revitalize and restore the building and install a cafe.
Union Station Women's Lounge
Open House Chicago
The long-vacant Women's Lounge just off of the Great Hall is hidden away in Union Station, one of the nation's busiest rail depots. A work of Beaux-Arts design, this Great Hall was originally designed by famed Chicago architect and city planner, Daniel Burnham.
Groupon
Open House Chicago
Though Groupon itself is less than a decade old, the headquarters for the daily deals site is housed in the historic former Montgomery Ward Catalog Warehouse. Typical of mid-aughts startup companies, the office space is packed with whimsical features like a swing set, an "enchanted forest" and a fake cat in a giant spaceship.
Warwick Allerton Hotel
Open House Chicago
The Allerton Hotel -- now called the Warwick Allerton -- was hope to the Tip Top Tap Lounge, which has been closed since the early '60s. The ballroom, which now can be rented out for private meetings, used to host the likes of Frank Sinatra and Lucille Ball.
Chicago Board Of Trade Vault
Open House Chicago
The Chicago Board of Trade vault opened to the public for the first time in decades in 2013. The vault re-opens to guests on the Open House Chicago tour for just the second time, and visitors can see where traders used to store everything from grain receipts to silver bars.
Sky-Line Dining Room
Open House Chicago
The members-only club on top of the Old Republic building was reconstructed from a pub first built in England. New renovations now include an open-air terrace with a 360 skyline view -- a major perk in what's considered Chicago's oldest private club.
The New Regal Theater
Open House Chicago
This 2,500-seat auditorium with Moorish-revival design has been mostly closed for most of the last decade. The site was originally the Avalon Theater, which opened in 1927. Sixty years later, it was renamed in tribute to the original Regal Theater on King Drive in Bronzeville. The one notable event to take place during the closure: The New Regal was the city of Barack Obama's election night victory party in 2008.
Caption information courtesy of the Chicago Architectural Foundation.
