When Al Pereira gets off the bus upon his arrival in Alicante, an audio report in Spanish, likely on radio, is advertising the Alicante release of the movie 'Alphaville, une étrange aventure de Lemmy Caution (1965)' mentioning it's "by Jean-Luc Godard, the director of 'À bout de souffle (1960)' and that it stars Eddie Constantine and Anna Karina. Since Constantine is also the star of this film, this breaks the fourth wall.
The film was shot in color but released outside of Spain in black-and-white.
The first in a long running series of films by director Jesús Franco featuring private detective Al Pereira. The other films are: Les ebranlées (1972), Down Town (1975), Botas negras, látigo de cuero (1983), Camino solitario (1984), Al Pereira vs. the Alligator Ladies (2012), and Revenge of the Alligator Ladies (2013).