Once you've gotten the quest from Anaximander, immediately head up to New Formello. If you haven't already talked to Nance in New Cotra about the surface, you might want to do it on the way to New Formello.
Once you reach New Formello, immediately go to the Inn and talk to Flanagan, who's sitting at the table near the door. Also talk to Dominique, who's standing at the bar, so that you can talk to Benedict next time you're in Krizsan to complete that quest.
Once youve gathered your information leave New Formello and head to the northwest. What used to be a passage ending in a blank section of wall should now have a Cave in it. Enter the cave, and immediately use the Light spell or some other form of illumination.
When the tunnel opens up into a larger room you'll be ambushed by a few Chitrachs. Once you've dealt with them examine the bodies near the western wall.
There's a secret tunnel in the northeast corner of the room. Follow the tunnel along. You'll come to a room with quite a few stalactites, which you'll have to make your way through. It's difficult, but not impossible, just keep trying different ways until you make it through.
Shortly after this the passage will again open up into a larger room. And again, there's an ambush, this time when you approach the eastern exit to the room. There's some Chitrachs, and some Null Bugs, so you'll have to count on physical attacks. Once you've dealt with this ambush go out the eastern exit and proceed along the passageway. There's a couple lines of lava, but they're easy to avoid. Look at the crystals scattered on the ground. The Fine Crystals mark fire traps, which will hurt your party, but there isn't any way around them. Just heal your characters if they start to get low on hit points. Pick up the Fine Crystals to sell.
Once you've passed all the traps you'll cross over a stone bridge. Right after the stone bridge is another room, with guess what? Another ambush. This is the largest ambush yet, with some Chitrach Larvae, some Chitrachs and some Null Bugs. Be aware that there's a Null Bug that's going to come up behind you. Once you've dealt with the ambush the only thing left to do is go over to the skeleton against the northern wall. You'll automatically pick up a twisted metal key.
Now it's time to leave the cave and head back to Fort Emergence. You might want to take the long way around so you can stop in Ghirka and tell Rentar-Ihrno about the Alien Slime. She'll give you a ring as a reward. Talk to Anaximander and he'll tell to hold onto the key, as it might prove useful. Once you're done we'll go back to the surface and complete the minor quests in Krizsan Province.