Sybil's Cave in New Jersey was forgotten for more than 100 years. Located on Castle Point opposite Manhattan, this New Jersey cave offered a great view to Manhattan on the other side of the Hudson River. Sybil's Cave was really a deep hole in the green veined serpentine rock of Castle Point, dug out to reach the small spring there, and later beautified by an archway of handcrafted stone. The sparkling spring water was sold for one penny a glass (a very high price then) and was said to have medical powers.

Today the cave is rediscovered, but still it is not reconstructed. The cave was declared unstable by an engineer, so the reconstruction work was delayed. The plans are to create a park at the hill around the cave and reconstruct the cave entrance archway. Although the arch was originally made of rock it will be reconstructed in wood.