After you get the Mysterious Machine up and running in Grounded, you will witness an explosion near the Oak Tree on the far side of the map. Your next mission will be to investigate this explosion.
This is tough, as there are many spiders in the area, and they will kill you very quickly. Thankfully, there is a place that will allow you to enter the area, you just need to make your way to a specific place on the map, shown above. Here, you will find a long tree root that runs from the Oat Tree to the edge of the grass, and you can run along it, bypassing the vast majority of the spiders in the area.
From there, follow the tangle of roots around to the area that is smoking, and here you will find a broken door. Head inside to find the Oat Tree Lab. Venture down the hallway, and you will come to a room with two locked doors. Pick up the cassette on the first console, the move the second console with the six buttons, and a switch. You need to turn all the six buttons green, then open the door by flicking the switch.
To turn them green, hit each button, and watch very carefully what other buttons change color. Unfortunately, there is no way to reset the buttons, so we cannot tell you exactly what order to hit them in to open the door. It shouldn’t take very long, as there are limited combinations you will need to try. The above video should be able to help you, however.
When the door opens, a small robot will attack you, and you can easily defeat it. Venture further into the lab to discover a new friend and an interesting secret.