This area will only show up once you've accepted the throwing mastery quest.
Outside (not shown)
The passage leading to K'na Tha is located east of where you start out.
1 - Chest
You'll find a boomerang in the chest. That's important here because you'll need a thrown weapon to make your way through the area, and some thrown weapons (like theaerial decapitator) don't have enough range. The boomerang does.
2 - Three Torches
You'll need to throw a weapon at the middle torch to advance to level 2. To do that, go into combat mode and then alt-click on the middle torch. If you attack one of the other two torches, you'll be teleported to the room with the chest (#1) and a level 12 ensanguine soul will appear. Nothing will happen if you kill the plaguish maiden guarding the torches.
3 - First Part of Level 2
All you'll need to do is kill a few things and break down some doors.
4 - Three Torches
Just like with the first trio of torches, you'll have to shoot out the correct one in order to move on to the next level. This time the correct torch is the rightmost one. If you shoot the leftmost torch you'll be teleported to level 1. If you shoot the middle torch you'll be sent back to the beginning of level 2.
5 - Starting Point in Level 3
6 - Unlit Torch
When you shoot the torch you'll be teleported to the next set of torches (#7).
7 - Three Torches
This time the correct torch to shoot is the leftmost one. If you shoot the rightmost or middle torches, you'll be teleported back to #5.
8 -Starting Point in Level 4
9 - Three Torches
The correct torch is the middle torch. If you shoot it you'll be taken to the final areas. If you shoot the leftmost torch you'll end up back at #5. If you shoot the rightmost torch you'll end up at #8.
The final areas are small (and not shown). Just loot the chests for some wonder drugs, fight creatures for a while if you want, and then shoot out the middle (lit) torch to be taken to an altar. You'll find Azram's Star in the altar. Then just shoot the nearby torch to be taken back to the world map.
A. Teleporter back to the world map.