Listen to Sarchel the Storyteller's telling of The Legend of Harclave: ( -95, -73, -174 ) /waypoint -95, -73, -174. You must be present during the final part of the story in order to receive the quest prompt.
If you die in the instance you will revive back at the entrance. However, if you didn't place a plank across the first gap, and don't have fast enough run speed, you may find it difficult if not impossible to jump the first gap. Try using the horn that sticks out from the side of the cliff if you need to jump.
Follow the path at ( -29, -72, -163 ) /waypoint -29, -72, -163 that leads to the Sundered Splitpaw: The Trial of Harclave; zone in and turn immediately to the left. Click the torch in the rock at ( 127, -51, -198 ) /waypoint 127, -51, -198 to pick up Harclave's Torch. Your first mission within this instance is to light eight braziers.
Proceed forward until you arrive at an impassable gap. Move the board at ( 123, -71, -155 ) /waypoint 123, -71, -155 to get across the gap and light two fires on this second ledge at ( 106, -70, -166 ) /waypoint 106, -70, -166 and ( 91, -69, -168 ) /waypoint 91, -69, -168. You will need to target the wood fuel inside the brazier.
Go down the ramp from ( 94, -71, -180 ) /waypoint 94, -71, -180. There are two fires in this chamber at ( 106, -78, -210 ) /waypoint 106, -78, -210 and ( 61, -78, -202 ) /waypoint 61, -78, -202.
Go up the far left tunnel from ( 93, -76, -265 ) /waypoint 93, -76, -265 to reach a ritual chamber. There are two fires on the ground in this chamber at ( 41, -66, -278 ) /waypoint 41, -66, -278 and ( 75, -66, -286 ) /waypoint 75, -66, -286.
Get the four boxes in this room, plus 2 boxes in the previous room, and stack them all to form a staircase and climb up to the Ark of Harclave, situated on the ledge in the back. Light the last two fires next to the ark at ( 50, -60, -316 ) /waypoint 50, -60, -316 and ( 60, -60, -317 ) /waypoint 60, -60, -317.
Examine the Ark of Harclave at ( 55, -59, -316 ) /waypoint 55, -59, -316 and you will be granted The Spirit of Harclave, a very strong buff that greatly increases your max health, max power, in-combat regen, and applies a damage shield akin to Brambles. It also decreases your experience gain by 90%. This will also spawn a group of six eternal Tesch Vals around the Ark.
The buff will not zone with you when you evac, die or leave the zone.
Next you need to kill a Zygomyd Spore King, at ( -2, -65, -182 ) /waypoint -2, -65, -182. Back near the first two fires you will find another wood board at ( 84, -70, -176 ) /waypoint 84, -70, -176. Use both boards to build a bridge and cross over the chasm. It's worth noting that there are multiple heroic encounters in this area. If solo, it pays to pull carefully, even with The Spirit of Harclave buff. If you can, pull way back, there are multiple wandering yellow groups.
If you fall down into the chasm while attempting to cross it, interact with the gear-like elevators located in the southwest.
Lastly, Rosch Val Gornas must be defeated, at ( -100, -63, -94 ) /waypoint -100, -63, -94. You will have to build a staircase of crates to reach his ledge. The crates can only be placed a couple times, as they weaken with each move, so build carefully. Once he is dead, click on the throne to complete the quest and be ported back out to Splitpaw Den.