Mystery In The Mountains - Act 3 Side Quest
Start Location: Shangshung Village
Quest Location: Tsongmo Peak
Objective: Defeat the named Neanderthals inside the cave in Tsongmo Peak
Mystery In The Mountains is a Side Quest which you get early on during Act 3. There are multiple NPCs that you can speak with to start this quest, the first NPC is in Shangshung Village which is where the Western Silk Road Portal will take you. Alternatively you can speak with the father in Chumbi Valley or the Son in Tsongmo Peak to begin this quest as well.
The part of this quest that takes place in Chumbi Valley is completely optional and will reward you no EXP except what you get for killing monsters. In order to complete this quest you'll want to head to Tsongmo Peak and go into the Mountain Cave which is located behind Da-wa Phu-ti, he's the son of the man in Chumbi Valley.
Inside of this cave you'll find 2 named Neanderthal Heroes, Yurg Rattlebone and Tor Skullcrusher. Both of these Neanderthal enemies are riding Sabercats so they're difficult to miss. At the end of this cave you will find an opening which leads outside to a small cliff. Here is where you will find another named, Barmanu who is the toughest of all 3.
Barmanu Strategy: This boss is arguably one of the hardest you've faced up until this moment. Depending on your build and gear he can one shot you with both his melee attacks or his meteor shower which he calls down from the sky. When he raises his arms up into the air (like in the screenshot above) you'll want to move as this is the animation for the meteor ability. The only other ability he has that you need to watch out for is his yell which works the same as a cyclops yell; it'll stun you for a few seconds after it hits you.
To turn in this quest return to Shangshung Village after Barmanu and the other Neanderthal Heroes are dead and speak with Kilu Tem-ba.