Hi WERY 8^)
Those stones relate to the Skeleton statue you wondered about. They describe the key to unlocking the gate behind the statue. There are buttons around the statue in East West North South... the cardinal points. You push the buttons in sequence once you have put the code together, but they screwed the puzzle up and repeated one, while omitting another.
Still, you can push the correct sequence and gain entry, where you must navigate an underwater path which splits into a couple of directions. One takes you to an alternate entrance to the cave just around the corner from the statue. The second path leads you to a secret room with a very cool prize after a 'suprise' battle against some skeletons.
The statue faces East, and the correct sequence is S.E.E.W.S.N.N.S.
Enter this as quickly and accurately as possible. Don't sweat it if you don't get it right away. It will work.
As for the cave with the wooden door in South Surdana, that's called Kragmor,and it's one of the cooler levels in the game.
When you get back from Surdana after opening the Ravenshold Eye, General Dehrimon tells you when you talk to him about a mission to take out a Wartok chieftan called Snotmaw.
That's the Kragmor mission.
Sometimes the game glitches out a little and you don't get it. No way around that except to crack through the mountain above the entrance and glitch/sneak in.
Try to read up on previous posts if you end up having to do that (in case Dehrimon doesn't give you the mission).