Background
South of the prison where you meet Steafan (in Kal'Hirol - Trade Quarter,) you can travel south down the path to where the runestone puzzle is. There are four runestone pillars and four runestone markers.
Walkthrough
In order to loot the sarcophagus in the middle of the room, you must solve the puzzle by clicking on one of the pillars (with one colored runestone) and matching it with it's mate of the same color and shape, so each pillar and runestone in front of it is the same. When all four are the same, the middle sarcophagus will be lootable.
Assigning places for each pillar and stone:
Solve: R4 > R5, R2 > R1, R1 > R5, R3 > R5
The order in which you do the clicking doesn't matter as much, as long as you match the runestones up. The above solution is simply a straightforward way of solving the puzzle.
Result
The sarcophagus in the middle of the room will be exposed, allowing you to loot it. Amongst the loot will be Gauntlets of Hirol's Defense and Nature's Blessing (neck piece.)