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Welcome! The door is open

Curious about what’s inside that old building you drive by every day? You’re in luck. The Doors Open program provides free access to buildings not normally open to the public.
Image: Atlantic Avenue Tunnel, NYC
Entry to NYC's Atlantic Avenue Tunnel, NYC is via a manhole, not a door. Bring your own flashlight. Jeffrey Donenfeld

The Empire State Building. The White House. The Tower of London. And, of course, Graceland.

When traveling, we often make a beeline for the homes of the rich and famous and to buildings that have historical significance. And there’s something appealing about reaching the top of iconic structures and walking onto observation decks offering panoramic views over a city.

But what about the places next door to those much-visited structures? Or that imposing church, government building, or residential mansion you pass by on your way to these tourist destinations? Or that shuttered factory or art-deco office building in your own home town? Don’t you sometimes wonder what’s behind those closed doors?

Well, now’s your chance. Thanks to a movement called Doors Open that began in Glasgow, Scotland, cities in the U.S., Canada and other countries around the world, now host events where the doors to normally off-limits spaces are flung open to the public — for free.

This weekend: Doors Open Denver
Billed as a celebration of the city’s built environment and design, the 6th annual Doors Open Denver takes place April 17-18. Organized by the city and county of Denver and the Denver Architectural Foundation, event manager Carol Hiller expects more than 50,000 people to visit the 80 to 90 buildings around town that are usually off-limits to the public.

“It’s a way for people to learn something about the history and architecture of the city,” says Hiller, “and because this year’s theme is adaptive re-use, they’ll get to see buildings being used in creative new ways.”

This year, participating sites include the city’s old main post office, which has been turned into a high-security federal courthouse; a restored mansion that serves as the Colorado Governor’s Residence; a theater in a former mortuary; a Yellow Cab garage that now houses businesses and residential units; and the Historic Sugar Building, which was built in 1906 as the headquarters for the Great Western Sugar Company and now houses office and retail space, and two original Otis cage elevators.

Image: Clock Tower, Denver
Visitors can tour the top

One sure-to-be-popular site is the Daniels & Fisher Tower, which was once the tallest building in Denver. The Italian Renaissance Tower has a restored lobby with marble floors and walls and a 17th floor boasting a giant clock-face and a balcony that offers great 360-degree views of the city, the surrounding plains and the mountains.

For those who can’t decide which buildings on the long list to see, there will be several lists with suggested themed sites to visit, a Box City where kids can request permits to begin construction of their own towns and non-stop pipe organ recital performed on a Wurlitzer installed in a local theater back in 1930.

More doors opened
If you can’t make it to Denver this weekend, don’t worry. Doors at many other usually off-limits locations will soon be opening in cities throughout North America, including Toronto, New York, Chicago, Lowell, Mass.

On May 13-15, the city will hold its 9th annual Doors Open Lowell event, and Stephen Stowell of the Lowell Historic Board says visitors will be free to peek inside up to 30 buildings, including many reclaimed and restored mill buildings, a 1920’s classical revival Masonic Temple “with curious chambers and meeting rooms,” and the subterranean space that once housed giant turbines for a power plant that ran a local mill.

During , held on May 29-30, 150 buildings of architectural, historic, cultural and/or social significance will be open to the public. Highlights include: Toronto’s City Hall, which offers self-guided tours of the Rotunda, the Council Chambers and the Observation Deck, and the five-story red brick Toronto Flatiron Building, which pre-dates New York City’s famous Flatiron building by about ten years. Also open to the public will be the Canada Life building, which has a weather beacon and a 17th floor tower room offering a panoramic view of downtown Toronto and Lake Ontario, as well as the restored circa-1920 Canon Theater — once the largest and most elegant vaudeville and motion picture palace in Canada.

Image: Buffalo City Hall
Buffalo City Hall, the country's largest city hall, offers tours during Doors Open Niagara.

New York, which does everything in a big way, will host the 8th annual Open House New York event this year on Oct. 9-10. More than 200 sites throughout all five city boroughs will participate, and executive director Renee Schacht says the event will include free walking and cycling tours, kids’ activities, performances, and much more. Not all of the participating sites are confirmed yet, but Schacht says there will be behind-the-scenes tours at Radio City Music Hall, historian-led tours of the Woolworth Building and other popular, if unusual, sites such as a wastewater treatment plant in Greenpoint and the Atlantic Avenue Tunnel, which is accessed not by a door, but by a manhole.

“There are no rats,” says Schacht, “There’s no water leakage and no sewage. It’s an old, abandoned train tunnel that has a constant temperature in the 60’s year-round. We tell people to bring their flashlights, but those who arrive with headlamps get the best views.”

Cross-border doors
On Oct. 17-18, between 75 and 100 churches, historic homes museums, and theaters will be participating in Doors Open Niagara. Put together by the Binational Tourism Alliance, this event straddles the U.S./Canadian border in the Buffalo and Niagara Falls region of New York and in communities around Niagara-on-the-Lake and Niagara Falls, Ontario, in Canada.

Image: Canon Theater, Toronto
The restored, circa-1920 Canon Theater was once Canada's largest and most elegant vaudeville and movie palace.

On the Canadian side, visitors can tour sites such as the Port Dalhousie Inner Range Lighthouse in St. Catherines and Queenstown’s Mackenzie Printery and Newspaper Museum, which houses the oldest press in Canada.

On the U.S. side, Doors Open participants will be allowed to tour Buffalo’s Electric Tower, which was built in 1912 as an advertisement for electricity, and the impressive 32-floor, art deco Buffalo City Hall, one of the largest city halls in the country. The building has exquisite, detailed murals in the lobby and an outdoor observation deck that offers views of Niagara Falls.

Future doors to be opened
Unfortunately for Chicago, which calls itself America’s first city of architecture and design, budget constraints eliminated funding for the city’s Doors Open-style celebration for 2010. However, the Chicago Architecture Foundation, which offers very reasonably-priced bus, walking, train and river cruise tours year-round, is already putting together funding for Open House Chicago 2011, which will take place on Oct. 14-16.

In the meantime, if you’re visiting Chicago or any other city, take a moment to look at the Web sites of local historical and architectural organizations before you go. Many of those sites have lists of historical homes, buildings and structures you can visit year-round on free or low-cost guided tours, or on self-guided tours with maps you can pick up in town or download from the Web.

And don’t be shy: if you’re curious about what’s inside a building, go up to the door, poke your head inside, and ask. You may end up on a private tour of a hidden architectural treasure.

Harriet Baskas is a frequent contributor to msnbc.com, authors the and is a columnist for USATODAY.com. You can follow her on .