Hey, I'm new here to the forums myself as well. Anyways, I just got pass this part (the lock and key quest) - towards the southeast part in Broken Valley there's a tower you enter and you talk to a Guildmaster I believe, he gives you a key - the key will get you you into the cave you need to enter. You'll know you're in the right spot because upon entering there's two enemies that start talking and then attack you.
If you look at this map, the area around 5.20 is where you need to go.
http://guides.gamepressure.com/divinityiiegodraconis/guide.asp?ID=8186
