I saw this movie in the early ’70s on TV in colour (garish, grainy Technicolor, if I remember correctly). It left an impression on me as I found some of the imagery extremely frightening, but I remember my feelings more than the actual scenes.
It was some kind of fantasy adventure where the heroes were on a quest, having to pass a series of perils to reach their goal and then make their way back. I vaguely recall a swamp-like peril, but my strongest memory is of a crack opening in the ground revealing a passage to a cave filled with thick white web-like material, home to some nasty creature I’ve blotted from my mind.
The heroes may have been led by a famous character like Hercules or Sinbad or Jason (the Argonaut) but I don’t specifically remember Harryhausen-like stop motion monsters.