help with campaign

Hi, i just recently got into dnd and im loving it so much i decided to make my own campaign for my friends that ive been playing with. I am getting a little stuck and need some ideas tho and cant find any through google or other reddit threads for the exact thing im looking for.

to paint the picture, essentially my friends will enter an underwater cave and theres gonna be some sort of stone golem guarding the next walkway through this cave. im sure theyre gonna try stealth checks and stuff to sneak past it but i need a backup idea for if it fails. i do not want the golem to fight them and id prefer if they didnt fight it, but who knows. i really am looking for like a riddle or puzzle or something of the sort or some form of conversation to go down between the golem and them. i havent gotten as far as figuring out what its guarding yet as im still working on the story and maps and such (im doing this all from scratch bc i love writing fantasy), so ideas on that would be cool as well. thanks!