Hidden Threats Quest/Spoiler

Required Equipment

 * Rope [or equivalent]

Method
Go to the deepest floor of the Venore Corym Cave and make your way to the northwestern area. Move along the northern wall until you encounter a new passage harbouring a teleport for you to enter. Do so.

You are now inside the Corym Mines. Walk up to Corym Ratter and say hi/help/yes. Now walk through the Sealed Door to the east and enter it. Keep moving north until you find Corym Servant. Progress by saying to him hi/decreased resources/defy. He wants you to free his fellow underlings so that they can stage a riot.

Go downstairs to enter an area with Stonerefiners. Walk northeast and enter the fiery room to encounter a Box (Quest). Open it to receive a Metal File. Now go south and take the first passage to the right. There's a Box (Quest) hidden behind an Item Pile in this room. Open it to obtain a Rusted Key Fragment (Head) and proceed further down the passage until you can go no further. Open the Box (Quest) here as well to obtain a Rusted Key Fragment (Handle).

Use the Metal File on both fragments to obtain a Polished Key Fragment (Head) and Polished Key Fragment (Handle). Take both fragments to the big room you had to traverse on your way to the first box and use them on the Steaming Hot Lava coming out of the Crucible to obtain a Glowing Key Fragment (Head) and Glowing Key Fragment (Handle). Use one of the fragments on the other to obtain an Intermediate State. Use this unfinished key on the Anvil to obtain a Forged Glowing Key and then use that on the tile of water to obtain a Forged Key.

Now go back upstairs and walk around until you've used the key on all three locked Sealed Doors around the mine. If you want, you can enter the rooms to receive a pair of Coal Eyes from the first NPC you talk to (per room).

Go back to Corym Servant after doing this and he will ask you to obtain 20 piles of Rare Earth. These are easily looted from the Stonerefiners below. Deliver them and you will receive 10 Platinum Coins.

That's the end of this quest. However, there's a surprise waiting for you once you use the exit teleport out of the mines. You will be teleported into a separate room containing three Tarantulas and the miniboss Cave Spider. It behaves like a Giant Spider, so just kill it and exit the room to officially end the quest.