Okay, the movie is "Jason and the Argonauts", it's from 1963 so there was absolutely no way this could have been done with CGI, and is Harryhausen's most famous stunt. Basically, the guy who did the first King Kong was his idol, he worked hard so one day he became his pupil and eventually surpassed his master, making them father and grandfather of kaijus/giant monsters.

You wanted a monster and doing a rubber suit wasn't feasible? Ray was your man. He's even referenced in Monster's S.A. (the fancy restaurant name, Harryhausen's, is a homage to him)

Here's a list of his monsters, coupled with small animations of them.

Ray Harryhousen, the master of Stop Motion, the inspiration for so many directors, and the creator of so many iconic creatures. May your works continue to be admired for years to come.