See inside some of the city's architectural gems at this weekend's event, which gives access to 150 of Chicago's best buildings

Main picture: New Regal Theatre by Eric Allix Rogers

When it comes to great architecture, Chicago has more than its fair share and there's no better time to explore some of the Windy City's architectural gems than during Open House Chicago, a free, city-wide, behind-the-scenes look at many of the city's great places and spaces.

Organised by the Chicago Architecture Foundation (CAF) and taking place over this weekend (October 18-19, 2014) the event gives access to 150 buildings and spaces including repurposed mansions, hidden rooms, sacred spaces, private clubs, iconic theatres, offices, hotels and more -- all for free.

Open House Chicago (OHC) gives you access to buildings that tell the stories of Chicago communities and cultures. By venturing into diverse neighbourhoods for self-guided exploration, OHC participants come together to discover community and place.

Most of the buildings are open between 9am and 5pm, though times for individual sites may vary. Details can be found on the website.

Here are 10 of the must-see Chicago buildings that will be opening for the event.

(text is from the Open House Chicago website, openhousechicago.org)

190 S. LaSalle

Photo: Eric Allix Rogers

The 190 South LaSalle building is both overtly postmodern and tastefully contextual. It was designed to pay homage to Burnham & Root's 1892 Masonic Temple Building (demolished in 1939). Philip Johnson and John Burgee's 1986 office building features an elegant, 45-foot, bronze vaulted lobby containing a wall-sized tapestry of Burnham's 1909 Plan of Chicago. The upper floors are capped by a chateau-like faux gabled roof. The richly decorated 40th-floor law library has floor-to-ceiling window views of Lake Michigan and the statue of Ceres that looms above the Chicago Board of Trade Building.

Edgewater Beach Apartments

Photo: Eric Allix Rogers

In 1928, Edgewater Beach Apartments was completed as the last section of the Edgewater Beach Hotel complex, which was started by Marshall and Fox in 1918. The apartment building was connected to the hotel by a three-block beach promenade. The hotel was demolished in the late 1960s -- a decade after the extension of Lake Shore Drive cut the hotel off from the beach and severely diminished business. The massive, pink, Spanish-style stucco apartment building is all that remains of the storied resort which hosted the most famous politicians and celebrities in the world for several decades. The apartment building, run as a co-op, is a unique Maltese Cross shape which provides most residents with a view of the lake.

Photo: Eric Allix Rogers

Groupon

Photo: JJ Jetel

Groupon is a global leader of local commerce and one of the fastest growing companies in history. The company was founded in Chicago in 2008 and now occupies several floors of the 1.25-million-square-foot former Montgomery Ward Catalog Warehouse. The historic building is a visual landmark that curves alongside the North Branch of the Chicago River. Groupon's colorful offices include such spaces as an Enchanted Forest, a Fun Zone with swing sets and a giant cat in a spaceship (the company's unofficial mascot). The office, designed by BOX Studios, was intended to reduce paper use and has minimal space dedicated to paper-based functions like printing. The open floor plan includes distinctly themed zones and meeting rooms.

New Regal Theater (Avalon Theater)

Photo: Anne Evans

This 2,500-seat auditorium opened in 1927 as the Avalon Theatre. It was renamed in 1987 as a tribute to the original Regal Theater on King Drive in Bronzeville, which was demolished in 1973. The "atmospheric" Moorish-revival design by John Eberson was similar to that of the Paradise Theater on Chicago's West Side, which was demolished in the 1950s. The theater was designated a Chicago Landmark in 1992. Despite holding an election-night party to celebrate Barack Obama's victory in 2008, the theater has been vacant and mostly unused since 2003. A mural on the western exterior of the building includes the likenesses of many famous jazz and blues musicians including Dizzy Gillespie, Louis Armstrong, Duke Ellington and more.

Photo: Anne Evans

Sacred Heart Schools, Driehaus Center (Conway House)

The Richard F. Conway House was completed in 1906 for the owner of the paving company that constructed Lake Shore Drive. The enormous Tudor Revival home is the work of architect William Carbys Zimmerman, who designed many nearby mansions on this posh stretch of Sheridan Road. Sacred Heart Schools purchased the house in 1959, using it for a variety of purposes and sparing it the fate that befell most of its neighbors. A $4 million restoration, completed in 2010, brought the house back to its original splendor, with beautiful oak and mahogany woodwork, ceilings beamed in unique geometric patterns, and no fewer than 19 restored leaded-glass windows. It now provides offices and event space for Sacred Heart Schools.

Sky-Line Club

Perched atop the Old Republic Building, the Sky-Line Club is one of the oldest private membership facilities in Chicago. Originally located in the Sussex region of southern England, the old ale house was carefully dismantled and reconstructed at its present site atop one of Chicago's early office high-rises almost 100 years ago. Paintings and furnishings from the original pub grace the interior today. From within the stately décor of the club, members have watched the city's skyline evolve into a 21st-century metropolis. The intimate space recently underwent renovation and also includes an open-air terrace with 360-degree views.

Sts. Volodymyr & Olha Ukrainian Catholic Church

Photo: Eric Allix Rogers

The eye-catching, gold-domed church visible from Chicago Avenue is actually quite new in comparison to the other grand churches of Ukrainian Village. Completed in 1973, Saints Volodymyr & Olha Church follows the Byzantine-Ukrainian style of the 11-13th centuries -- with a strong preference for circular patterns and avoiding almost all angular designs. The exterior of the building features a mosaic above the entrance depicting the Christianization of Ukraine. The interior is one of the grandest -- yet intimate -- churches in the city, with its vibrant red, blue and gold color-scheme and attractively-designed stained glass.

Photo: Eric Allix Rogers

Studio V Design (Krause Music Store)

Photo: Steve Hall of Hedrich Blessing Photography

This building was commissioned for the Krause Music Store in 1921 and was architect Louis Sullivan's final project. Today, it is home to Studio V Design, a firm that specializes in integrated marketing communications and brand design. The green terra cotta facade, with its elaborate plant forms and geometric patterns, is one of Chicago's most recognizable storefronts. After decades as a funeral parlor and 15 years as a storefront, the building was purchased in 2005 by Studio V Design. The new owners, Peter and Pooja Vukosavich, embarked on an extensive restoration and renovation project with Wheeler Kearns Architects. Starting with an interior that was essentially a blank slate, the architects transformed the space into an elegant, flowing office -- culminating in a private zen garden at the rear.

Photo: Eric Allix Rogers

The Forum

Photo: John Morris

The Forum was built in 1897 and contains possibly the oldest hardwood ballroom dance floor in Chicago. This imposing red brick building played a significant role in Bronzeville's cultural scene by hosting performances of music luminaries -- including Nat King Cole -- and by providing space for civic groups and political meetings. After 40 years of vacancy, the Forum was deemed unstable and hazardous to passersby. It was nearly demolished in 2011. New owners, Urban Juncture, bring fresh energy to the movement to rescue the Forum and plan to open a café and restore Forum Hall.

Union Station

Photo: Eric Allix Rogers

Union Station is the third-busiest rail terminal in the United States and the only intercity rail hub in Chicago. Most of Union Station is underground, but the headhouse building on Canal Street is the architectural focal point of the nearly 10-block complex. The project was started by Daniel Burnham in 1913 and completed by the firm of Graham, Anderson, Probst and White in 1925. The magnificent Beaux-Arts Great Hall is one of the busiest rooms in Chicago. But, unbeknownst to many, some fascinating parts of the station's long, storied history are hidden behind closed doors just feet from where more than 120,000 commuters pass by every day.

Photo: Eric Allix Rogers