The Essex County Hospital Center is an abandoned mental hospital / facility in Cedar Grove, NJ. It's main years of operation were from the late 1800's to the early 1900's. The complex is huge, spanning approximately 90 acres and features approximately 15 buildings, some of which are very large. Many of the buildings are connected through a network of underground tunnels.
According to historical records, 24 people died over a few weeks time in the hospital due to suffering from extreme cold in 1917 due to downed climate control.
The site is now supposedly haunted, and has appeared on multiple paranormal TV shows.