Answer by taking a quote from the following article:

Khalid El-Masri (also Khaled El-Masri and Khaled Masri, Levantine Arabic pronunciation: ['xa:lId el'mas?ri, -'mas?re], Arabic: khld lmSry) (born June 29, 1963) is a German and Lebanese citizen who was mistakenly abducted by the Macedonian police in 2003, and handed over to the U.S. Central Intelligence Agency (CIA). While in CIA custody, he was flown to Afghanistan, where he was held at a black site and routinely interrogated, beaten, strip-searched, sodomized, and subjected to other cruel forms of inhumane and degrading treatment and torture.

After his release, in 2006 El-Masri wrote in the Los Angeles Times that, while held by the CIA in Afghanistan, he was beaten and repeatedly interrogated. He also said that his custodians forcibly inserted an object into his anus. He was kept in a bare, squalid cell, given only meager rations to eat and putrid water to drink. According to a report by the inspector general of the CIA, El-Masri's German passport was not examined for authenticity until three months into his detention. Upon examination, the CIA's Office of Technical Services swiftly concluded it was genuine and that his continued detention would be unjustified. Discussion over what to do with El-Masri included secretly transporting him back to Macedonia and dumping him there without informing German authorities, and denying any claims he made. In March 2004, El-Masri took part in a hunger strike, demanding that his captors afford him due process or watch him die. After 27 days without eating, he forced a meeting with the prison director and a CIA officer known as "The Boss". They conceded he should not be imprisoned but refused to release him. El-Masri continued his hunger strike for 10 more days until he was force-fed and given medical attention. He had lost more than 60 pounds (27 kg) since his abduction in Skopje. While imprisoned in Afghanistan, Masri befriended several other detainees. The men memorized each other's telephone numbers so that if one was released, he could contact the families of the others. According to the New York Times, Laid Saidi, an Algerian who was a former detainee, was released in 2006. His description of his abduction and detention closely matched that of El-Masri. El-Masri reports that Majid Khan, characterized by the Bush administration as a high-value detainee, was held in the Salt Pit at the same time as he was. Khan, a former resident of Catonsville, Maryland, was held by the CIA for an additional three and a half years prior to being transferred to US military custody and Guantanamo on September 5, 2006.

what is the salt pit?
high-value detainee, was held in the Salt Pit at the same time as he was.