Morgan uncle's tavern:
When you first arrive In the level 3fight off all the pirates on the first street. After you fight them all, go to the right to find Morgan's uncle's tavern.

Advance to level 4:
Begin game play in two-player mode. Reach level 2 and have player one enter the first wooden door at the same time that the player two enters the dark door that is next to the wooden door. Press Up simultaneously on controllers one and two to advance to level 4.