This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

Harlem park dedicated to compulsive hoarders killed by their own junk.

The competition: breathe deeply as long as you can.

Protecting the future of some of the rarest and most misunderstood mammals of North America.

Hop on the train and tour an elaborate miniature town made completely of junk (including the train).

The end of the 4 Line is also the end of the line for 300,000 souls in one of NYC's most illustrious cemeteries.

Self-sufficient greenhouse floating on the Hudson River.

The home of one of America's most wealthy industrialists is now a historic site that remembers a more decadent time in the country's history.

The loneliest island in New York.

Glacial erratic or man-made dolmen? It probably wasn't druids.

This stately estate house features a tower covered in a bright, modern mural.

One of Scotland's most important modern structures, it just made the '100 Most Endangered Sites' list.

Largest lake in Great Britain measured by surface area.

This dilapidated castle-like structure overlooks the Hudson River at one of its widest points and was once home to nuns.

Oldest existing church in New York and the inspiration for Washington Irving's "The Legend of Sleepy Hollow."

The only intersection in America where the buildings on all four corners were built pre-Revolutionary War.

100 massive sculptures in the Hudson River Valley.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

Small monoliths of several varieties of stone sit alongside a wooded path in the Bronx.

America's greatest forgotten garden and the former stomping grounds of Son of Sam.