History of Violence

Achievement can only be done while on the garrison daily.
Thak the Conqueror's Bust is located at 41.2, 12.2.

In the order to get the other three relics, use Jewel of Transformation to transform into an ogron and then you will be able to break boulder piles. Breaking one boulder pile will unearth one of the following items:

Thurg the Slave Lord's Necklace
Krog the Dominator's Hammer
Gorg the Subjugator's Idol
Unearthed reliquaries
Blazing crystals.

EDIT: edited for clarity.

The bust is at 41,12. Don't waste 30 minutes hunting in boulders like I did...

/way 37.63, 15.75
/way 35.50, 15.90
/way 36.54, 20.32
/way 36.50, 20.30
/way 38.20, 13.60
/way 37.50, 20.40
/way 36.61, 17.00
/way 40.72, 24.91
/way 39.50, 16.70
/way 36.50, 16.80
/way 37.80, 18.10
/way 37.83, 18.09
/way 38.80, 16.44
/way 35.42, 22.54
/way 40.70, 15.20
/way 39.76, 14.49
/way 38.10, 24.44
/way 37.59, 23.23
/way 35.40, 22.70
/way 37.42, 16.06