How to open the underwater door of sunken forest land

The way to open the underwater door of the sunken forest land is to build a trebuchet in it with a modifier, press E up and down and the door will open.

The game is introduced:

This game is a horizontal adventure game. I like the style of this game very much. It's warm, including BGM, which makes people feel very comfortable. It is a rare good game.

Game background:

The background is set in a forest called niebuhr Mountain, and the patron saint of the forest is the "Elf Tree". In a storm, Ori, a child of the Elf Tree, was blown off the tree and adopted by Naru, a wild animal in MengMeng. The elf tree killed three young birds and a black bird of Li Shuhang. In order to find the light from the Ori, only an unhatched egg was left in the descendants of Li Shuhang.

Li Shuhang took the core of the elf tree and threw it away. Elf trees slowly withered, and forests in niebuhr began to wither. Naru, the beast who adopted Ori, starved to death, and Ori died of depression. The Elf Tree revived the Ori with the last magic, so the Ori embarked on the journey of reviving the Elf Tree.