20 hours cave diving for what part? Not a single part is found in caves.

Ancient Bark - Swamps
Ymir Flesh - See the trader
Iron - Swamps, and else where soon.
Drauger Elite Trophy - Well that's an easy romp in the swamps at a Drauger spawn pile; come to think of it, you could possibly get one at the Drauger spawn piles in the meadow as well.

I mean it's not like this game has .003% drop rates (or worse) like in other games I have played.