There are three exits - one stairwell, one teleporter to tower level 3, and one teleporter to Thera's Temple.

You cannot kill Khull Khuum (he is, after all, a god).

You can finish the game regardless of whether you trap Khull Khuum or not. You can use the 4 silver object to trap him.

Spoilers

Press shift-F8 to display current location.

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Start @(6,6)

- 4-item teleporter @(6,6) to/from tower3 @(6,1)
- 4-item teleporter @(5,14) to Thera's Temple. You can only use this after you have all 9 planetary orbs, and are also carrying all 4 of the silver objects.

- Khull Khuum @(5,10). You cannot kill him (Kill a god? Not likely!). You must visit him to win, as he is carrying the last two orbs. I have finished the game two different ways, one by running away, the other by trapping KK.

Method 1. Approach KK from the N. After he finishes his first speech, take the orbs. When he finishes his second speil, and is quite upset, run past him, to the S, and through the teleporter to Thera's temple.
Method 2. Place silver items on the small circles to the N, E, and W of the square KK will appear on. Do this from the outside, not from the square he appears on. Step onto his square from the S. When he finishes his first speil, take both orbs. When he finishes talking again, take 1 step back and place the last silver object on the small circle in front of you. This traps KK and places him in his own orb (just like the other gods).
- There are other ways of trapping and misleading Khull Khuum.