Whoa, the basement was a ton of work. Now it's finished. Tested with my followers. Some behavior is a bit strange, but this has to do with the shape of the interior: The planks, grates and pillars are difficult to handle, there is no plain walkway. And they refuse to use the stairs. No matter what I tried with the navmesh or with the stairs (it's a fixed part of the interior, so I can't do much about it), they use another method to get to the "loft": The simply move up or jump down, lol!