Hendler's Sanitarium was a fictional mental health hospital located on Long Island, New York. This facility was mentioned in Dangerous Grounds.

After spending four years studying psychiatry in Europe, Doctor John Rawley returned to America and accepted a posting at this mental health hospital. He expected to find a place that provided mental therapy for the patients; however, he was deeply disappointed by what he witnessed at this hospital. According to him, Hendler's was an experiment wherein the wealthy could indulge in their delusional fantasies while spending an inordinate amount on money on a place that was little better than a country club. While he was there, as a staff member, Dr. Rawley first met Charles and Serena Wilson. They were patients at the hospital. After six months, the doctor quit the sanitarium. (TNG: "The Big Goodbye")

The pages seen in the episode were from the mystery novel Dangerous Ground by author Frances Sil Wickware. This novel was published in 1946. Information on Hendler's Sanitarium was from pages 13 and 23.
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