City throws open its doors to public.

New York City's rich architectural, design, engineering and cultural heritage will be on display this Saturday and Sunday as openhousenewyork (OHNY) presents the 7th Annual openhousenewyork Weekend, October 10 and 11

The event offers free access to sites in all five boroughs showcasing everything from the historic to the cutting edge.

More than 175,000 people are expected to participate in the event, which in past years has drawn audiences from both the Big Apple and all 50 states and many nations around the world.

"For nearly a decade, openhousenewyork has opened the eyes of millions of New Yorkers and visitors to the city alike to the astounding architecture and design to be found in New York," said Renee Schacht, executive director of OHNY.

"This year, we are thrilled to feature private residences, historic landmarks, architect and artist studios, and new sites that demonstrate sustainable design."

Among the participating sites are tours of the Apollo Theater, recently renovated by Beyer Blinder and Belle Architects; the Atlantic Avenue Tunnel--the world's oldest subway tunnel; the newly opened High Line designed by James Corner Field Operations with architects Diller Scofidio + Renfro and, rising above it, the Standard Hotel by Todd Schliemann of Polshek Partnership Architects;

All listings, including changes and additions, will be available online at www.ohny.org beginning October 1.

An opening party for OHNY Weekend will be held at The Visionaire, a new participating site and the greenest residential development in the United States, on Friday, October 9, from 7-9 pm.

The Visonaire, designed by Pelli Clark Pelli and developed by the Albanese Organization, received a LEED Platinum certification from the U.S. Green Building Council.

In addition, OHNY will raffle a behind-the-scenes-tour of the Woolworth Buildlling, led by resident historian Roy Suskin and the author of The Skyscraper and the City: The Woolworth Building and the Making of Modern New York, Gail Fenske. For more information about OHNY Weekend, including the OHNY Weekend Passport, visit www.ohny.org