It's never a good thing when a US space expedition crashes off the coast of Sicily, bringing with it specimens from the planet Venus. Nothing good can come of it. It's time for a Ray Harryhausen creature of the week and this is one of his best creations. Ray never named the monster in the film, but he called it a "Ymir":
Never named in the film, the Ymir is a native of Venus. Returned to Earth as an egg, the Ymir rapidly grows to monstrous proportions in Earth's atmosphere and runs amok.
This was one of my favorite monster movies of all time.
Here's some trivia:
20 Million Miles to Earth was in production in Rome, Italy in September 1956, using only William Hopper of the main cast, and in the U.S. from October 30 to November 9 of that year. Rome was chosen as the location for filming because Harryhausen wanted to vacation there. The working title of the film was The Giant Ymir, and it has also been released as The Beast from Space. In the released version of the film, the creature is never referred to by name, as Harryhausen was concerned that audiences might confuse "Ymir" with the Arabic title "Emir".
Ray Harryhausen wanted the film to be shot in color, but the filmmakers were not given a budget large enough to accommodate color film. In 2007, five years after the death of the film's director, Harryhausen worked with restoration and colorization company Legend Films to create a colorized version of the film. That version, along with the original theatrical black-and-white version, was released as part of a 50th Anniversary Edition of the film on July 31, 2007.