A Cure For Wellness ((full)) Direct

A young executive, Lockhart, is sent to retrieve his company's CEO from a mysterious "wellness center" in the Swiss Alps. The center is a Gothic castle turned spa. Once there, Lockhart becomes trapped and discovers the facility's horrific secret: its director, Dr. Volmer, has been using the patients' biological fluids to sustain his own immortality, dating back to a baron in the 18th century. The "cure" involves forcing patients into eel-infested water tanks to "purify" them, while the director exploits their suffering.

If you're looking for a of the film's plot, themes, or ending, here it is: a cure for wellness