The Yarna Desert was deathly hot, and at the entrance to the desert Link saw two huge skulls, left behind by ancient monsters. Link fought Leevers and moving cacti until he came to a place where the sand slowly drifted down into a hole. Link heard an evil voice from below roar at him, telling him that he was only an annoyance getting in the way. A huge Lanmola burst out of the sand, and Link jumped in to attack. The sand slowly bore Link towards its center, but Link used Roc's Feather to jump around. The Lanmola dove in and out of the sand, and Link slashed at its head whenever it came out. When the Lanmola was defeated it dropped the Angler Key, which, unfortunately, was quickly sucked up into the sand. Link dove in after it, and fell down into a cavern. Luckily, the Angler Key was lying on the floor right next to Link, so Link took it and got out.

Outside, Link read a statue on which was inscribed:

SEA BEARS FOAM, SLEEP BEARS DREAMS. BOTH END IN THE SAME WAY CRASSSH!

Link couldn't figure out what it meant, but he was noticing that many things on Koholint Island related to sleep and dreams. He was about to leave the desert when the owl flew out of no where, telling him that

The shape of the key shows a fish, swimming up a cascade of water! Go now to the mountain waterfall! A leap from the top and you will reach your goal!

Link realized that the river's source was in the mountains to the north, so he heeded the owl's advice and headed toward Tal Tal Heights. In front of one of the waterfalls Link found a keyhole, and put in the Angler Key. The ground shook, and the face of a fish sculpted out of the cliff face was exposed as the waterfall stopped flowing and water was drained away from the entrance. Link couldn't get to the entrance directly, though, so he climbed the mountains looking for a way in.

While searching around, Link found Papahl, the father of the quadruplets in Mabe Village. Papahl had told Link earlier that he was going to get lost in the hills, and he had done just that. Now he was so famished that he couldn't move, and he begged Link for some food. Link gave him his pineapple, and Papahl scarfed it down as fast as he could. Out of gratitude, but not as a reward, Papahl gave Link a flower he had found, a hibiscus. Link recalled that a certain female goat in Animal Village would like to have this flower...

Link tucked the flower away and continued searching. After wading through knee-deep water, he at last found an exposed cliff right above the entrance, and remembering the owl's words, he jumped off. Link landed right in front of the entrance, and went into the Angler's Tunnel through the mouth of the fish's head. The cavernous tunnel was deathly quiet and flooded with knee-deep water. Cracked blocks got in Link's way at first, but he set up bombs next to them and blew them to smithereens.

An owl statue told Link that the glint of the tile would be his guide, but Link didn't yet understand this clue. He explored the cavernous tunnel, staying away from deep water, until he was trapped in a room with Cue Ball, a huge octopus. Cue Ball scooted around a watery track, and Link used Roc's Feather to jump over the octopus and strike him in the back of the head. Link was getting exhausted from so much jumping, but finally Cue Ball was defeated and a door opened up. In the next room Link obtained a pair of Flippers, with which he could now swim in deeper water.

Now that he could swim underwater, Link was better able to look for the fourth Nightmare. He found a set of tiles, one of which glinted, and observed that stepping on it made another tile glint. Stepping on all the tiles in this manner made a door open. Later, when he found a similar set of tiles, he stepped on them in the same order, and was able to move on. In an underground tunnel, thwomp blocks tried to crush Link, but he waited for them to fall and start rising again and brushed past them. He even jumped on one to reach a high step. Link finally found the Nightmare Key, and started to look for the Nightmare's Lair.

Entering a dark, dank cavern, Link jumped into some dark water. Swimming slowly to the bottom, Link was frightened to see a human skull at the bottom, and even more frightened when he noticed a huge Angler Fish, the fourth Nightmare! This ugly fish was hungry and, wanting to eat Link for lunch, made a lunge at him. Link made a great effort to swim out of the way in time to avoid the fish's jaws, and hit him with his sword. By now the mother of all angler fish was calling in little baby fish to attack Link, and rubble was raining into the water from the cavern ceiling. Now Link had to simultaneously avoid three dangers while trying to hit the big Angler Fish.

The Angler Fish's outer skin was hard and bumpy, so it was a long battle before Link could finally pierce it with his sword. The Angler Fish was eventually destroyed, and Link resurfaced and exited the cavern to claim his prize. An opened door gave Link access to the Surf Harp, which soothed him with its smooth notes. As Link warped back outside, the mysterious voice told him that his road went into the bay...

Back outside in the sunlight, Link saw another cave in the cliffside a little way off. Two fish were carved above the cave entrance, and Link swam through the water until he reached the cave. He swam inside and was confronted by a huge fish and two smaller ones. Link was about to turn around and get out when the big fish spoke. His name was Manbo, child of the Sun Fish, and seeing that Link had an Ocarina, he taught him his song, Manbo's Mambo. Link couldn't help but laugh at the fish's silly, gyrating dance moves. The song Link learned allowed him to warp to Manbo's Pond, a small pond in the middle of Koholint, or to the entrance of any dungeon he happened to be in.