Follow the man's instructions and make your way through the cave. It won't be hard to complete. Once finished head back to Elcid. Once there, talk to Tia. You will later hear about monsters in the Cave to Sundletan. Just go north of town and you will find the cave.

** One thing the game doesn't mention is that if an enemy runs into you from behind, the enemy gets to attack before you can. If an enemy is chasing you, turn around and fight them. **

Go to Cave to Sundletan > (N/A)