ok so maze does not work. good to know
It doesn't work if you take the iron part as the maze and the void as 'walls' either (select PROP tool, type, any element that doesn't look like IRON, then flood-fill directly on any part of the iron. If it doesn't all change, again parts of it aren't connected to the rest)
Easy way to check is switch to heat view (for clear visibility) then flood-fill with PLSM. If there are places that don't get filled, they're closed off
It's not. All the edges are closed and it's full of dead ends