Your free guide to New York's architectural treasures

The Waldorf-Astoria Hotel may have been barricaded and locked down when President Bush stayed there during the Republican National Convention, but for one weekend in October the Presidential Suite will be open to all comers - and they needn't pay the starting price of $7,500 per night.

At the second annual Open House New York, more than 100 buildings in all five boroughs will give doormen and ticket takers the weekend off while letting the masses troop through for no charge. The sites range from a rustic 17th-century Quaker meetinghouse to the cutting-edge Austrian Cultural Forum, a tapering tower of glass and steel.

There are also monuments and arsenals for the historically minded, while engineers may relish a climb up a water tower or the descent to a steam-driven power plant.

During last year's inaugural event, about 45,000 people took advantage of the opportunity, and organizers expect this year's event, on Oct. 9 and 10 (the second weekend of the month), to be even more popular.

"I think of it as an urban safari," says Scott Lauer, executive director of Open House New York. "In almost any place you go, New York included, it's easy to forget what's around you and what you're walking by every day. This gives people an opportunity to stop and look around, look up, look inside."

While each person's peripatetic exploration hinges on personal taste, Mr. Lauer hopes the experiences will add up to a greater understanding of New York's man-made environment. With so many architectural proposals on drawing boards across the city - including the World Trade Center redevelopment - he feels that encouraging discourse on design is almost a civic duty.

"Our mission is to attract the broadest, largest audience possible to learn about and experience this history, these examples of good design," says Lauer. "That's why it's important for [the event] to be free, and it's important for it to be citywide."

Those who already have a thorough understanding of architecture also benefit from the tour by gaining access to places that are usually off-limits, says Rick Bell, executive director of the New York chapter of the American Institute of Architects, whose Center for Architecture will serve as the welcome center during Open House New York.

"Seeing something firsthand, rather than through a slide show or the snippets presented through the media, is the difference between seeing a game at Yankee Stadium and listening to it on the radio," says Mr. Bell.

Open House New York's excursions are perhaps most pleasing when they satisfy a long-held curiosity: What arcane altar might lurk inside the Grand Lodge of the Masons on 23rd Street? While the reality may disappoint conspiracy theorists, the lavish interiors and ornate details are certain to delight architectural buffs.

The site list also includes many museums and cultural institutions that are usually only open to the public for a fee, but which agreed to the freebie weekend as a way to reach out to a new audience. Many site sponsors had heard of the similar open-house events in London and Toronto that garnered rave reviews and huge crowds, and guessed rightly that the New York incarnation would be equally successful.

But the common motivation expressed by museum directors, monument caretakers, and designers is that they have long recognized the grandeur of their building or space and take pleasure in sharing it with the public.

The Terrapin Chelsea Art Gallery is one of the few private homes on the list, although it does double duty as a gallery. Owners Pamela Harvey-Rath and Colin Rath know they have a special house: They gutted an old brownstone and created an urban oasis outfitted with a two-story waterfall and a scale model of the Yangtze River that winds through their living room.

"Everyone says, 'I can't believe you're opening your home to strangers,' " Ms. Harvey-Rath says with a laugh. "But we like to show people what we've done and what can be done, and hopefully inspire them to do something creative themselves."

All the openness and welcoming may seem downright unnatural in these days of hyper- security. But that state of affairs is exactly what makes Open House New York so necessary, says Lauer. "This event in some ways is an antidote to the lockdown mentality that many of us feel,." he says, adding: "It shows that we're still able to say, 'Come on in.' "

• The list of sites to be visited this year is available online at www.ohny.org or, on Oct. 9 and 10, at Open House New York's weekend headquarters at the Center for Architecture, 536 LaGuardia Place. Call (917) 626-6869 or e-mail info@ohny.org for more information.