What psychiatric facility houses Eurus Holmes in The Final Problem?

Sherrinford is the psychiatric facility and government black site where Eurus Holmes is held in “The Final Problem.”

The episode reveals that Eurus, Sherlock and Mycroft’s exceptionally gifted sister, was first sent to a mental institution after the apparent death of Sherlock’s childhood friend Victor Trevor. Mycroft later arranged her transfer to Sherrinford, a maximum-security prison in the North Sea described as a “prison within a prison.”

Sherrinford is not one of the ordinary London institutions mentioned elsewhere in Sherlock. Bart’s is the hospital where Molly Hooper works, Pentonville is a real London prison, and Baskerville is the military research facility featured in “The Hounds of Baskerville.” Those names can therefore seem plausible but refer to different parts of the series’ world.

At Sherrinford, Eurus has manipulated staff and gained extraordinary control over the facility. Sherlock, John Watson and Mycroft travel there to confront her, leading to the episode’s elaborate psychological tests and deadly games. After Sherlock reaches her emotionally, Eurus is returned to Sherrinford, where Sherlock later visits her and communicates through music rather than conversation.