Currently at level 4, wiped out with no enemies left. Went in circles through the whole labyrinth but for the life of me I can't find the entrance to the 5th level. There are 2 closed doors, double clicked on them, dragged them and they don't open, they don't even make a locked sound. There's also a passage with a barred gate near the portal, but there's no switch or lever nearby to open it, also tried to double click and drag it with no avail. So, how do I get to the next level?