I learned from the website, Forgotten NY that the hulking elm in the Northwest corner of the Washington Square Park used to be used for hanging executions! This grisly use came to an end in the 1820s, when Rose Butler was hanged for arson
Actually, some say hers is the only recorded hanging that took place there and that the tree's deadly history is largely an urban myth.
The park's scary side doesn't end with the tree though. Excavations in the late 1800s turned up old corpses beneath the park from the former burial ground which use to lie there. Thousands and thousands of bodies still lie under the walkways and fountain. Skateboard on that!