The interesting part here is the sluice port.
What about it?
What to do?
I have the gear
It is too rusty
I have the oiled gear
It is filled with water
There is a door down there with climbing rocks. But the handholds don't go near enough?
Use the machinery. There is that gear that you need, first.
Try out the machinery with it. You can insert it to one of the slots (and remove it) to get that handle to work.
You need to oil the gear.
Now, the right handle will pump some water into the sluice. The left handle will move the gate up and down.
Fill it with water...
Henrik will lower the gate with the left handle and pump the water in with the right handle. Move the oily gear, also.
Great! Now Tove can climb down and head into the tunnels.