How to Reach the Shrine
To find this shrine, you need to have at least one empty sword slot, bow slot, and shield slot.
Go to Keo Ruug Shrine to reach the Korok Forest. Go northeast from the Master Sword pedestal and follow the bean lamps. Talk to Damia the Korok and tell him that you are ready to start the Test of Wood.
He gives you the Forest Dweller's Sword, the Forest Dweller's Shield, and the Forest Dweller's Bow. You have to keep them equipped and not lose them throughout the trial.
Don't worry about the countdown at the beginning. This trial is not timed.
If you get sent back to the beginning of the trial area, the enemies that you killed earlier will stay dead.
In the first area, a few Keese will attack. Your Forest Dweller gear has low durability, so avoid using it. Instead, try using remote bombs to kill the enemies in the area.
When you approach a fence, some Chuchus will pop out of the ground. Go east along the fence. There will be a wall of wooden crates. Use a bomb to get rid of the crates.
Some fire keese attack in the next area. If you hit them with your sword, be sure to put your sword away (press B) afterward to put out the fire on the sword.
There is also a Stalkoblin in this area that shoots regular arrows at you. If you need arrows, raise your shield and let the Stalkoblin shoot at you, then put your shield away to collect the arrow.
Farther ahead, some Stalkoblins will shoot ice arrows at you.
Beyond that, an electric chuchu will pop out. Be careful not to let it shock you, because you could drop your weapons or shield and be disqualified.
Then there is a bog where Octoroks will spit rocks at you. If you bounce rocks at them with your shield, be careful not to let your shield take too much damage. You can use Cryonis to put pillars directly on top of the Octoroks if they are under the bog's surface (if they jump up, just wait for them to go back down before putting a pillar on top of them). There is a chest in this area that contains another Forest Dweller's Sword. You can switch to it without being disqualified. You can get through this area by climbing the trees. You can try climbing to the top of a tree and floating past the area altogether, but you run the risk of going out of bounds and being sent back to the start of the trial.
The final area is another bog. Fire Chuchus will appear if you try to jump from island to island. There is also a Stalkoblin that will shoot fire arrows at you. But you can use this to your advantage by riding the updraft if the Fire Chuchus or Stalkoblin set the grass on fire.
When you get close to the shrine, Damia the Korok will congratulate you. Go to the shrine and examine it to open it.
Treasure Chest in the Shrine
The chest in the shrine contains a Giant Ancient Core.