Pilgrim Psychiatric Center
“Pilgrim Psychiatric Center, formerly known as Pilgrim State Hospital, is a state-run psychiatric hospital located in Brentwood, New York. At the time it opened, it was the largest hospital of any kind in the world. Its size has never been exceeded by any other facility, though it’s now far smaller than it once was.
By 1900 overcrowding in New York City’s psychiatric asylums had become a serious problem. There were several strategies implemented to deal with the escalating patient overload. One was to put the patients to work, farming in a relaxed setting on what was then rural Long Island. The new state hospitals were dubbed “farm colonies” because of their live-and-work treatment programs and emphasis on agriculture. However, these farm colonies, Kings Park State Hospital, (later named Kings Park Psychiatric Center) and Central Islip State Hospital (later named Central Islip Psychiatric Center), became overcrowded, like the institutions they were meant to replace.
New York State began making plans for a third farm colony, which was to become Pilgrim State Hospital, named in honor of the former New York State Commissioner of Mental Health, Dr. Charles W. Pilgrim. The state bought approximately 1,000 acres (4.0 km2) of land in Brentwood and began construction on the hospital in 1929. Pilgrim State Hospital opened on October 1, 1931 as a close-knit community with its own police and fire department, courts, post office, a LIRR station, power plant, swine farm, church, cemetery and water tower, as well as houses for staff and administrators. A series of underground tunnels were used for routing utilities. Each set of buildings were known as quads, a pattern of four buildings situated around a center building, where the kitchen was located.
The hospital continued to grow as the patient population increased. Eventually, the state of New York bought up more land to the southwest of the facility to construct Edgewood State Hospital, a short-lived facility that was a subsidiary of Pilgrim State Hospital. In fact, Pilgrim State Hospital was so large that it reached into four Suffolk towns: Huntington, Babylon, Smithtown and Islip, and had two state roads passing through its bounds.” — from Wikipedia
There were allegations of patient mistreatment, which may have been worse than any other institute of its kind. Due to this, it is considered to be a haunted location.