1. The Boyd Theatre
Philadelphia, Pennsylvania

This "major motion picture palace," which sits in downtown Philadelphia, opened in 1928 and operated until 2002.

Now, it sits vacant and, since it lacks designation as a historic landmark, is threatened with demolition and neglect.

2. California's State Parks

California is home to the largest state park system in the United States, which boasts 278 parks (including 51 designated State Historic Parks), covers 1.5 million acres and protects 295 miles of oceanfront. However, its vast array of historic and cultural resources is at risk from chronic underfundng and deferred maintenance.

3. Charity Hospital and the Adjacent Neighborhood
New Orleans, Louisiana

The Art Deco design of this once-prestigious medical training and public health care facility is only part of its allure. It also served a legendary role in serving hundreds of thousands of uninsured patients. The building, which was surrounded by flood waters from Hurricane Katrina, has been vacant for three years -- and is now vulnerable to deterioration and demolition.

4. Great Falls Portage
Great Falls, Montana

The Great Falls Portage -- a National Historic Landmark along the Lewis and Clark Trail -- marks the location where, in 1805, Lewis and Clark maneuvered around the Great Falls of the Missouri River. The construction of a coal-fired power plant in front of the site is now threatening to damage the cultural and visual landscape.

5. Hangar One, Moffett Field
Santa Clara County, California

Hangar One was built in 1932 to house U.S. Navy airships, and was transferred to NASA in 1994. However, a 2003 inspection showed toxic PCBs are leaking from its metallic exterior, and while the Navy is responsible for environmental remediation, it is not obligated to preserve the building. It is now in danger of deterioration and neglect.

6. The Lower East Side
New York, New York

This legendary neighborhood was the first home for many immigrants since the 18th century. However, rapid development is threatening to erode the rich history, culture and architecture that the neighborhood is known for.

7. Michigan Avenue Streetwall
Chicago, Illinois

This 12-block stretch of historic Michigan Avenue dates back to the 1880s and is a "virtual encyclopedia of the work of the city's best architects." Designated a Chicago Landmark in 2002, this "streetwall" is still vulnerable to development projects that retain only small portions of the original buildings or their facades. Development projects have also been proposed that would disrupt this stretch of the historic Chicago skyline.

8. Peace Bridge Neighborhood
Buffalo, New York

The collection of homes in Buffalo's Front Park, Prospect Hill and Columbus Park neighborhoods date back to the 1850s and are a "catalog of American domestic architecture." However, expansion of a transportation plaza for the Peace Bridge, which connects Buffalo on the U.S. side of the Niagara River with Fort Erie in Canada, is threatening the area.

9. The Statler Hilton Hotel
Dallas, Texas

This now-vacant hotel was considered the most modern hotel in the United States when it opened in 1956. This "icon of mid-20th-century design" is being threatened by encroaching development.

10. Sumner Elementary School
Topeka, Kansas

Sumner Elementary School, a National Historic Landmark because of its place in the Civil Rights Movement (it was the centerpiece of the U.S. Supreme Court's (1954) ruling in Brown v. Board of Education), has been vacant since 1996. It has suffered damage from water infiltration, neglect and vandalism, and resources have not been allocated to help stop the deterioration.

11. Vizcaya and Bonnet House Museum and Gardens
Miami, Florida and Fort Lauderdale, Florida

These two historic house museums from the early 20th century are threatened by adjacent high-rise development.