How to discover hidden architecture

Once a 1930s milk depot, Quay House was converted in 2001 into an architect's studio and home. The structure is one of more than 800 buildings, neighborhoods and events featured in London's September 20-21 Open House event.

London's "Gherkin" is among major London skyscrapers to open. Visitors will have a chance to tour the foyer and top of the 40-story, curvilinear landmark.

Groupon's colorful offices in Chicago include an Enchanted Forest, a Fun Zone with swing sets, and a giant cat in a spaceship. You can tour the office during Chicago's Open House event, October 18-19.

The 190 South LaSalle building in Chicago features a richly decorated 40th-floor law library with floor-to-ceiling windows and views of Lake Michigan.

The Creative Arts House in Perth, Australia, is a quirky warehouse affectionately nicknamed the "LoveNest." Open House weekend in Perth starts November 1.

A free tour at the Port of Brisbane will let visitors see how an efficient and sustainable port operates. Brisbane will host Open House events October 11-12.

The XXXX Brewery will be open during Brisbane Open House. Visitors will gain insight into the 135-year history of the Queensland beer icon.

Horizontal House is a family home on a slope overlooking the ocean in Thessaloniki, Greece. Its exterior and interior are characterized by modern lines and spheres. Thessaloniki Open House takes place October 17-19.

Made of stone and wood, Solid House in Slovenia features a bookshelf that doubles as stairs to its upper level. Slovenia will host Open House events October 3-5.

This ecological resort in Slovenia was built over an abandoned gardening space. Glamping tents allow guests to live close to nature without sacrificing luxury.

The design of the Cultural Centre of European Space Technologies in Vitanje, Slovenia, was inspired by the 1928 plan for the first geostationary space station.

The Neustadt Collection of Tiffany Glass in New York displays pressed glass used in beautiful Tiffany lamps, windows and other works. Open House New York takes place October 11-12.

The joint headquarters of Norway's state rail company and the Gjensidige insurance firm won a major Norwegian architectural award in 2014. Oslo held its Open House event September 12-14.

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• London's Open House Weekend throws open doors to 800 properties


• Among them are landmark skyscrapers such as the "Gherkin" tower


• Open House weekends are now held in 20 cities around the globe

(CNN) -- If there's one thing better than snooping around a stranger's home, it's snooping around a stranger's home without being arrested.

This weekend in London, there's a rare chance to do just this with more than 800 normally-closed landmarks, including architecturally interesting family houses, throwing wide their doors to the public.

It's all part of Open House London, an annual event now in its 22nd year that lets thousands of people wander around and gawp at some of the city's most impressive buildings -- as well as some lesser known gems.

Often there's also a chance to meet and chat to the architect -- and it's all free.

The weekends have proved so successful, they've been adopted by 24 cities around the world, including Melbourne, Buenos Aires and Oslo.

Open House Worldwide scatters its events across the calendar, potentially allowing globetrotting architecture addicts to hit several in the space of a few weeks.

Following London's September 20-21 showcase, October sees New York follow suit, alongside other destinations such as Lisbon, Dublin, Chicago, Barcelona and Thessaloniki in Greece.

This year's big draws in London are expected to be some of its tallest skyscrapers -- among them the gherkin-shaped 30 St. Mary Axe and another giant known as the Cheesegrater.

Churches, cinemas, theaters, colleges, government buildings and subterranean top secret wartime bunkers are also included.

There are also numerous homes, including one of the country's most recognizable -- the Prime Minister's residence at 10 Downing Street.

Definitely worth a snoop.

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