That's a bit vague but here's my best advice:
Did you see some cutscenes with your fellow dragon explorers as you travelled down there?
If not, you missed something. Go back to the Quiet Meadow Inn, go upstairs, and the door on the far right. Talk to the li'l guy in his room.
If you did do and see that, you need to go up the cliff with the glowing jump sigil, down into the slug den hole... and look for a hole that leads you deeper.
Or you can just lose to the slugs down there, they'll take you to the boss.