The hospital Sandy Dennis escapes from is on Welfare Island, today called Roosevelt Island. Early in the episode Lt. Parker drives his car on the lower level of the 59th St. bridge from Manhattan towards Queens responding to the scene. You see him turn off mid-span onto a terminal on the north side of the bridge. He drives onto a vehicle elevator which lowers him onto the island. That no longer exists.
Anthony Zerbe's TV debut.
Welfare Island was originally known as Blackwell's Island, named after the original family that owned it.
It was renamed Welfare Island in 1921 and Roosevelt Island in 1973. In the past, the city build a number of institutions on the island, including a prison, an insane asylum and hospitals. Nellie Bly, an investigative journalist posing as a patient in the insane asylum, wrote an expose, "Ten Days in a Madhouse", which triggered asylum reform across the US in the late 19th century. Some hospitals remain, but the island began to be developed for residential use in 1968.