Torture, as a concept, is barbaric, designed to dehumanise an individual to the point of hopelessness and loss of concept of self.
The most effective form, that I have witnessed, is sleep deprivation. This has the effect of making the brain confused in function and blurs the lines of reason and memory. The subject loses the capacity to rely upon themselves.
Nature is full of examples of torture - orcas teaching their pups to hunt for seals, cats toying with prey and keeping them sufficiently alive as to be amusing, foxes rampaging through chickens etc
Torture can work and has been effective.
Guantanamo Bay is in Cuba for a very good reason!