July 9, 2025 1:42 AM (GMT+2) There’s a boat. So it seems like you should be able to use it to get to the other side. However, when the reservoir is fully filled, you cannot get to the boat. When it is almost fully drained, the water level is way too low. I best bet is that it has to be almost full, with only 1 or 2 bars missing, and then you can access the boat.

July 16, 2025 1:56 AM (GMT+2) I managed to leave the reservoir on the desired water level (well, at least what I very arbitrarily guessed is the desired water level), so at least I know it is possible:

However I could not go and actually see it because I hadn’t drafted Tomb.

Even though now I have access to the basement through the fountain, the problem is that to fully drain the fountain, everything else has to be completely full. Except if I can make use of the reserve tank (which I suspect can be activated by procuring it with steam power).

Thus, I’ll be trying to test that hypothesis, because it doesn’t only help with this, but also with What is at the bottom of the Reservoir?.

July 24, 2025 1:49 AM (GMT+2) I actually got to the other side of the Reservoir through The Foundation. I’m starting to have doubts that some arbitrary level of water actually makes the boat accessible and usable. I still want to try it for science, but I’ll lower the priority of this mystery significantly, since it’s now a bit useless to me.

August 9, 2025 9:01 PM (GMT+2) I got a chance to try this out without even really aiming for it. Turns out the game is designed in such a way that if you fully fill the reserve tank and drain the pool, then the reservoir’s water level ends up being just 1 bar short of full. I went there to see if the boat is usable at this water level, and the answer is… yes! It can be used. Although it’s not very useful to me since I already have all other shortcuts unlocked. But it’s good to know that this is also an option. Mystery solved! See Boat at the other side of the reservoir as a “souvenir” of the adventure.

August 19, 2025 8:40 PM (GMT+2) And yet again I found a piece of evidence after having already solved a mystery. In this case, Reservoir water levels is the hint that actually tells you the correct water level to be able to cross the reservoir with the boat.