Hub 3: Orchard of Lamentations

Walkthrough
It would be quite hard to explain it exactly but in practice, it is pretty simple. Take the only way available. It twists a bit, passes across a river of mud (beware of the Stalker there) and eventually leads to a roughly triangular-shaped area with lots of walls and high ledges around you. There again, although it looks like a maze, you in fact have only two possible ways to go, both leading to the same area with small alleys forming a cross in its middle. There get rid of all the monsters (as I suppose you did all the way here). If you stick to the ledge as you enter the area, you can walk all around it, picking up the goodies on it.

Then, take again the only possible way, i.e. through the southern alley to the switch at the end that lowers a platform to the lift room. There you will notice that the whole room lowers and quite quickly comes up again, crushing every monster (including you) that doesn't make it to one of the platforms that are all around the room. So the strategy is simple - pull the switch, quickly jump into the room and run to another platform. Let it take you up, kill the Ettin/s there, pull the switch there and take another run for another platform (I found out the most you can do is to skip one platform during one lowering). When you get to the other side, the platform there contains two switches. One lowers the room as usual and the other lowers the central part of the room, releasing some Dark Bishops. In that central part you will again find two switches, one of which lowers some walls in the triangular-shaped area. When you get there, you will see that the three walls on the east gradually lowered forming a very broad staircase that takes you to a small lake of mud where the Emerald Planet is. Take it.

Now get back to the cross-shaped area. Be careful, as the northern wall opened and released some monsters. Furthermore, if you step into the room thus revealed, the walls on its side will open too and let free some more monsters (of course giving you some pickups as well). After that, just take the eastern and western alleys that should now be lowered as well. There again, there is a map shift that breaks the geographical logic of the level a bit as each of those alleys leads to one of the two western ledges in the triangular area. The western one leads to a ledge with a magic amulet and the eastern one, most importantly, to a ledge with yet another Planet, the Sapphire one.

Those two Planets are all you're gonna get from this level, so now just head back to Heresiarch's Seminary.

Tips

 * Here, just as in any other level where they can be found, you can smash the mushrooms and they will produce a poisonous cloud that works just like when the Cleric uses a fléchette (quite useful for getting rid of Centaurs and Slaughtaurs, if you manage to get them to gather around a mushroom).