After completing the Dancing Dragon Dungeon, the Maku Tree says that he had a vision of a lake shaped like eyeglasses. This lake can be found east of Impa's house.
Back to Subrosia
Go north from Horon Village, then go north again from Impa's house. Go east from there, then north and east again. You should be in the screen where you danced with Din at the beginning of the game.
Go south and use the Roc's Feather to jump over the holes. Swim to the southeast corner of the area. There is a portal to Subrosia there. A sign says that you can only pick the petrified mushrooms in fall. Go into the Subrosian portal.
In Subrosia, you can go west to find the furnaces. However, the Subrosians say that everybody went to the temple to gather large rocks.
Get the Bomb Flower
You can go to the southeast area to find out how many signs you have broken. You can use Ember Seeds to break them, or blow them up with bombs. Later you can get a sword that breaks signs. Vasu will give you a ring after you have broken a certain number of signs. However, the ring doesn't do anything. It's just a trophy.
Go south from the portal that you arrived from. You will eventually reach an area with a volcano. Jump over the holes and continue south. Use the Roc's feather to make your way around the narrow strips of land. Fire Pokeys come up from the lava in some areas. You can kill these with your sword, but watch out for fireballs.
At the end of the lava area, you find something buried in the ground. Use the Power Bracelet to lift it. It's a Bomb Flower. It doesn't go into your inventory. It's shown on the screen with the rings and gasha seeds and trade sequence items that you have collected.
Get the Power of Autumn
Now go back to the screen with the house of the Subrosian who tells you how many signs you have broken. Go west from there. Jump over the lava, then go west and north. Lift the rock, then use a Pegasus Seed and the Roc's Feather to jump over the gap of two holes.
Go to the Temple of Seasons. Go to the northeast and jump over the lava. Talk to the Subrosian with the headband. He will use the Bomb Flower to open the path to the northeast tower. Before he leaves, he says to go to the furnaces if you need any ore melted.
Go inside and jump north to the stairs. Go up and continue on to the altar. The Spirit of Autumn will add the Power of Autumn to the Rod of Seasons. The Spirit mentions that in Autumn, pits are filled with fallen leaves, and mushrooms can be picked.
The Rod of Seasons now has the power of all four seasons.
Go to the Next Dungeon
Now go back to Eyeglass Lake. Go to the tree stump that is north and east from the cat in the tree. Use the Rod of Seasons to turn it to Autumn. Go south, jump over the holes, and swim east. Get on dry land and go north twice, then east. Pick up the mushrooms with the Power Bracelet (if it isn't Autumn, go to a tree stump and turn it to Autumn and come back here) and go into Unicorn's Cave.