After you get the Hawk Eye in the Pyramid, you reach the southern desert.
Get the Key
Go northwest from the small pyramid and talk to the man with the spear to get the Key to the Tower. Then go north and talk to the man to upgrade your equipment. Get the French Fry Pan for Paula. The man also sells Multi-Bottle Rockets, which are even more powerful than Big Bottle Rockets. You can also get the Bazooka, which does the same damage as a Bomb, but you can reuse it as many times as you want.
Go northwest to find a human-shaped tower. Prepare your ears for some weird music, then use the Key to the Tower to get in.
Explore Dungeon Man
There are monsters in here, but they are all fairly weak, and there are several places to heal up for free.
Go north from the entrance, then go to the left. Check on the bench to recover your HP and PP. You can go into the hospital on the left if you need status ailments cured or mushrooms removed.
If you want to have room for all of the treasures that you can collect in Dungeon Man, make sure that there are ten free spaces in your inventory.
Then go east, and go north along the east wall to find a gift box that contains Molokheiya Soup.
Go south again, then go north up the slope. At the bench, go west to find a gift box that contains a Cup of Lifenoodles. Then go back to the bench and go south.
After the slope, go west and north. When the path splits, go south. Open the gift box near the sign to get $5. Go up the slope nearby and when the path splits, go to the right to get a Snake. Then go north to find a Super Plush Bear.
Go back the way you came until you have gone down the slope. Then go west and north. You find four ropes. Go up the third rope. In the next area, when the path splits, go to the left to find a gift box that contains $10. Then go east again until you reach the wall.
Go south until you reach the south wall, then go west, then go north when you can. Climb up the rope, then go south to get a Pizza. Then go north into the area to the left of the rope to get a Sudden Guts Pill. Then go farther north to find a PSI Caramel. Then go up the rope south of that gift box.
Then go east, and from there, go as far south as you can go. Then go west to get a Wet Towel. Go back east, then go up to where the path splits, and go west. Go up the rope at the end.
Go north and talk to Brick Road. Then go south and drop down the hole that you find. Keep going down the holes. Open the gift box on the way to get an IQ Capsule. Then drop down the nearby hole to reach the first floor. Go south to exit Dungeon Man.
Dungeon Man will now be following you. He can easily defeat the monsters that you encounter.
Go south. If you want the Photo Man to take your picture, walk to the right of the pond that is south of where you first found Dungeon Man.
Then keep going south until Dungeon Man gets stuck in some trees.
Go east and talk to the man with the spear. He says that you need a submarine to reach the Deep Darkness. Go back into Dungeon Man. Make your way back up to Brick Road's face, and talk to him. He says to drop down the other hole on this floor. Go south, then east, to find that hole. Fall in, and keep falling through the holes you find. When there are no more holes, go east to get a Talisman Ribbon. Then go west and follow the path until you reach Brick Road's collection. Use the Instant Revitalizing Device to heal up, then check on the yellow submarine. There will be a cut scene.