Angler's Tunnel is hidden behind the Tal Tal Heights waterfall on Koholint Island. In order to enter, Link must first acquire the Angler Key, which is guarded by a Lanmola in the Yarna Desert. To enter the desert, he must get Marin to sing to the sleeping Walrus, which blocks the desert passage, in order to wake it up and make it move.
Once he has entered the desert and defeated the Lanmola, Link can take the Angler Key and use it to stop the flow of the waterfall, revealing the entrance to Angler's Tunnel. Once the entrance is exposed, he must climb the mountain into which it leads, then jump off the edge in order to land in front of the entrance.