×It's pretty obvious where you have to kill the golem:
Click here to view the secret text
×20,18
The trick is to realize that to get the golem stuck at that square, you need to get the 4 surrounding trapdoors dropped except 20,17, and it's only possible to get the golem there if you go back out the passage to 20,20 with the golem at the left to move the golem down from 20,17. The overall plan is as follows:
Click here to view the secret text
×Drop all the trapdoors except 20,17 and those on row 15.
Click here to view the secret text
×Lure the golem at 17,17, and use the trapdoor at row 15 to escape (point sword S). The golem should now be on 18,16.
Click here to view the secret text
×Go back down to 20,20 to move the golem to 20,18, which allows you to kill it on 20,17 as the last trapdoor.
