The devil's tuning
"Temples" or "finares" is the name given to alternative tunings for string instruments which facilitate or simplify their playing. They have always been very popular, first in Europe and later in America, where chordophones were introduced in the 16th century.
Among South American popular musicians there has been plenty of talk about the so called "temple del diablo" (literally, "the devil's tuning"), a very special tuning for the charango and the guitar that allows for open chord playing. It was said that when this tuning was used the guitar "plays itself" (without any fingers on it), and the singer-player was therefore able to not pay attention to the various left-hand positions which should otherwise be used to play certain tunes in certain tunings.
The origin of the term is linked to a set of legends and folk tales which suggest that the musician's skills would be directly associated with devilish agreements or, at least, the Devil's influence. This collection of stories includes traditions such as the one about the Salamanca (Argentina), a cave where, during the witches' Sabbath, singers, players and dancers would go in order to acquire new skills in return for their souls; or the one related to certain payadores (singers) from the Río de la Plata who are said to have made deals with the Devil to prove themselves unbeatable in song contests.
The "temple del diablo" would originally have been a gift from the Devil to one of his protégé, a singer who sold his soul to play the guitar to win his beloved one. After sealing the deal, the Devil took the instrument in his hands and tuned it in such a way that no effort was required to achieve chords which would be otherwise impossible using basic fingering schemes. The singer-player won fame and acclaim; however, according to tradition, he was never able to win the heart of the one he loved.
Article. "El guitarrero", by Eduardo Falú and León Benarós. In Folklore del Norte [es].