'I've had a look at that key you found. See here, it is etched with the runes for...let's see, the style if old. "Flame". That's it, it means Flame, or perhaps Fire. And this one is Deep, or Deeps, or wait, "Chasm", I Think.
'I think this one I've managed to solve for myself, at least in part. I imagine he is referring to the great chasms and flames found in the area near Anazarmekkhem. I know a clever dwarf by the name of Gapi, who has been posted there; he may be able to help you. Let me warn you, though, the trek there is very difficult and would take you either through the Waterworks to the south of here and then eastwards, or though Zelem-melek and the southwards. That is assuming they are still alive by the time you reach them. You may wish to wait until you are more experienced with the ways of Khazad-dum before heading there.
'That is the best advice I have. Now, if it is all the same to you, I have more records to study, and Falgeirr's maddemimg riddles have taken up enough of my time, thank you!'
Ondott has deciphered the runes marked on the key you found as meaning the Flame or Fire, and Deep of Chasm.
Talk to Gapi about the key you found
Gapi is at Anazarmekhem. You can take the path through the Waterworks, far to the south of the Deep Descent, and then eastwards, or through Zelem-melek and then southwards.
Ondott suggested that you take the key to his friend Gapi, but warned that both paths to the Orc-watch are very dangerous.