Hello @YellowUser. Thanks for sharing. This is quite a nice looking level. It really does look like a ventilation shaft. Well done.
Welcome to the forum. I give you 3.5 stars because of the lowest ball (it's very hard to push). Looks very much like a ventilation shaft like what @IceBlade said above and a striking resemblance to Fan Control by @P_simorf. Thanks @YellowUser