Christopher Lee's mummy walk isn't entirely acting. Besides the injuries to his back and shoulder noted above, he also injured his knees and shins while doing scenes in the studio-tank "swamp" - he couldn't see where the various pipes and fittings under the swampy water were.
Hammer Films had already done remakes of The Curse of Frankenstein (1957) and Horror of Dracula (1958). This was the first film made after Hammer reached an official agreement with Universal (then Universal International) allowing them to do remakes of their classic horror films. In this film, for example, the agreement with Universal allowed them to use the name "Kharis".
Although intended as a remake of The Mummy (1932), the film's plot and most of its principle characters are taken from The Mummy's Hand (1940) (1940) and The Mummy's Tomb (1942). The 1932 film's famous and early scene of the sight of the mummy walking across the tomb floor driving a member of the archaeological team insane is recreated here but not seen in any of the 1940s series; the finale of The Mummy's Ghost (1944) is also interpolated into this picture's plot, albeit with a somewhat different outcome. Despite all this, there is no credit to any preexisting source material at all.
Director of photography Jack Asher wanted to create the impression that the tomb had not been opened in thousands of years. So he had a crew member climb into the catwalks above the set to spray the air with water before each scene. As the water particles descended, they would take all the smoke and dust with them, leaving the air completely clear.
In Spain was released in 1960 in Madrid and Barcelona. In 1993, for your TV premiere was a new dubbing. And in 2016 was a re-release in Barcelona (Phenomena) for 1 day in subtitled version and 35 mm. copy.