Berserker Treasure Quest/Spoiler

On the first underground floor of the cave you will only face Orcs, Orc Spearmen, Poison Spiders and Orc Warriors. Make your way to the far south end of the floor and drop down to -2.
 
Here you will meet Poison Spiders, Orc Spearmen, Orc Warriors and probably one or two lured Orc Berserkers. Get to the crossing and quickly drop down to -3, avoiding any unnecessary trouble with the orcs.
 
As you come down, you will almost instantly be attacked by multiple Orc Warriors, Poison Spiders and one or two Orc Berserkers. It is recommended to use AoE runes or spells, e.g. Berserk/Groundshaker if you're a knight and Stoneshower runes if you're a mage or paladin. After fending off the attack, walk east and drop down another hole.
 
Down the hole you will meet up to 6 Orc Berserkers. AoE runes or spells are recommended. Slowly make your way to the eastern end of the floor, fighting off more Orc Berserkers and 1-4 Orc Leaders. The reward is in a box at the end of the floor, as shown on the map.
The Bottom room just before the room with the White Pearls has multiple Orc Berserkers and Orc Warriors. There are Two boxes below there where you can also find a Barbarian Axe and a Scimitar.