The Torre de los Alumbres was built in 1510 to protect Rodalquilar from Berber pirates who frequently made incursions along this coast to acquire water, minerals and people to sell as slaves. In 1520 it failed to repel a pirate attack and many of the inhabitants of Rodalquilar were captured and enslaved. It was abandoned in 1590.
I am under the impression that the bell tower was something constructed for the film.
Groggy and his men arrive
riding out to El Paso
Leone would use this location again for Duck You Sucker!, even adding a tower, only to promptly blow it up.
The actual interior of Indio's hideout was shot in a church in Turillas. I didn't make it there on this trip! Below are some additional photos, including the interior. Click to enlarge.