1980's movie help

I am trying to find the name of a movie about a bunch of kids and a teacher that get kidnapped by a couple men, I know one of them wears a santa mask. They end up in this underwater cave trying to escape.

Thanks for any help.

Ask here in the "What's this Movie?" thread.

the name is fortress. loved that movie watched it as a kid and it scared the mess out of me and my siblings. we would play it for days.