If you no longer have a set of mourner's clothes, you will need to obtain another set by killing a mourner on Arandar Pass. Warning! When you attack a mourner, all of your combat stats will be reduced to 20.
The mourner's top will need to be washed, and the trousers will need to be mended. To wash the top, steal some soap from the laundry basket near the druid washing clothes in Taverly. The trousers will require two silk and a piece of bear fur. They will then need to be taken to the seamstress in Lletya.
Talk to Arianwyn in Lletya first to tell him the mourner's plans. Then, head to the Mourner's HQ in West Ardougne and climb down the ladder. You will need to be wearing full Mourner gear to enter.
Talk to the Head Mourner in the south-eastern room. He will ask for your help to find out what happened to some of the excavation teams. Enter the door to the west, and follow the path all the way west. You will come across the dig team, dead. There will be level 73 shadows around them. They have low health, but attack accurately with melee.
Search the dead guard that is leaning against the wall. You will find a journal and color wheel. Return to Arianwyn in Lletya.
The Black Crystal
Arianwyn will ask you to help restore the safeguards on the Temple of Light. He will ask you to return a part of a large crystal that will be found in the temple.
Return to West Ardougne, and follow the same steps to get to the Temple of Light. Enter the temple, then head up the stairs immediately nearby. Go straight south, and climb up the ladder on the wall. Go north, then slightly west, and go down the stairs then. Go up the other stairs, then head east. The blackened crystal will be in the mid-east part of that floor.
Use your chisel on it to obtain a blackened crystal, then return to Arianwyn. You will show him the crystal, and he will summon Eluned to chant a replacement. Use the crystal on Eluned to give it to her. Talk to her again and she will give you a newly formed crystal.
Talk to Arianwyn again. He will tell you to take the newly formed crystal to the old altar to give it the power to safeguard the temple. Return once more to the temple of light.
Go up the stairs at the entrance, then go east of them. You will see a crystal collector on the wall. Note: This is a safe area from the shadows. Pull it, then collect all the items. Use a mirror on the nearby pillar, then search the mirror and rotate the mirror to the north.
From the pillar the light just went into, place another mirror, and rotate it so the light shines west. Add another mirror into the next nearby pillar, and have it shine south.
On the next pillar in the line, use the yellow crystal on the pillar to change the light to yellow. On the next pillar, place the last mirror and have it facing east. The yellow light will cancel out the blue light door, making it white.
Now, climb the wall supports to cross the gap. Having high agility for this is recommended, as you will likely fail often. If you fail, you will appear on the floor below. Simply run back to the entrance of the temple and climb up the stairs, then run south to repeat.
Enter the door of light and search the chest for more mirrors and a cyan crystal. Return to the collector.
Pull the collector, then collect everything. Put a north facing mirror in the first pillar, westward facing mirror in the second. In the third, place the cyan crystal to turn the light cyan. In the next pillar, place a north facing mirror.
In the next, place a eastward mirror, followed by the yellow crystal to change the beam to green. The green beam will negate the magenta door of light. Enter the door of light and collect the two mirrors in the chest. Return to the collector and pull it.
Return to the collector, and take the mirrors if you haven't already. Following the beam of light, direct the beam in the following order: North, west, yellow, north, east, up (make sure a beam of light is pointing up from the pillar).
Climb up the nearby ladder. Place a mirror in that pillar and rotate it west. A pillar there with a magenta crystal in it will turn the light red. Climb back down the ladder and head back towards the staircase to the far south. Climb up, go north, down the stairs then up the other. Head to the northwest corner.
Place a mirror in that pillar, and make sure it's pointing south. Then follow the beam all the way south, and place a mirror in the pillar. Make sure it is rotated like shown below.
On the second floor, from the collector, head southwest. Directly west from the stairs, you will see a wall you can climb over. This is also a safe area. You will also see a hole in the floor. On the other side of the whole, attach a rope to the rocks and climb down.
Head west. The red light will have opened the cyan door. Open and loot the chest.
Return to the collector, pull the lever and take the mirros. Following the beam of light, direct the beam in the following order: North, west, cyan, north, east, up (make sure a beam of light is pointing up from the pillar).
Climb up the nearby ladder. Place a mirror in that pillar and rotate it west. A pillar there with a magenta crystal in it will turn the light blue. Climb back down the ladder and head back towards the staircase to the far south. Climb up, go north, down the stairs then up the other. Head to the northwest corner. Place a mirror in the pillar and rotate it so it looks like the below:
The beam will be directed down to the bottom floor. Return back down to the ground floor and head all of the way to the northwest corner. A yellow door will have been unlocked for you. Rotate the mirror in that pillar south. Enter the other door then loot the chest.
Go back through the door and rotate the mirror back east so you can get out. Return to the collector.
Pull the lever and get your mirrors. Following the beam, place the mirrors going: North, west, south, yellow, east. This will once again open the blue light door.
Climb the wall supports to cross the gap. Once you finally get across, place the blue crystal into the pillar. Return across the gap, and take back the mirror nearest the gap and the yellow crystal.
The third pillar should direct up. Go to the third floor, and place a mirror in the pillar and direct it south. On the other side of the stairs, place the fractured crystal into the next pillar.
Following the east beam, place a mirror in it and make it face down by making it face like the following:
Following the south beam, make it go east. Then at the corner pillar, have it go down by rotating it like this:
Return all the way to the first floor, and find the green beam (a pillar on the second floor turned the eastern beam green). Direct it south, then east to open the magenta door. Place a mirror on the pillar there and direct it north to unlock the yellow door. Open and loot the chest.
Bringing it all Together
Pull the lever and collect everything. First pillar facing north. This time, the second pillar needs to be facing down.
Head to the bottom floor, and find the beam of light. Put a mirror in the pillar and direct it east. From that next pillar, put one of the fractured crystals in it. Follow the beam south and put the other fractured crystal in the next pillar.
From there, put mirrors into pillars east and west, and have them both going up. Go to the far north and place a mirror going up there. On the second floor, go to the north where you just directed that beam and place the yellow crystal in the pillar. Climb up the ladder and place a mirror there going west.
Climb back down then head south and climb up the stairs to reach the third floor again. On the pillar nearest the stairs, place a mirror in it and direct the beam west. Two pillars east, place a mirror in there and direct it west. On the next pillar, direct it north.
Get to the other side of the stairs, and direct the beam west. Place the blue crystal in the next pillar. Go to the far northwest corner. Direct the beam south. Follow it south, then in the next pillar, direct it east.
Return to the middle of the two stairs, then go down to the ground floor from there. The cyan door will finally be open. Search the pillar and direct the red beam of light to merge with the others. Go through the newly opened doors of light.
NOTE: If you have to leave to get after this point, you will either have to rotate the red beam of light around to unlock the cyan door again, or use the 'back way' through the Underground Pass! This back entrance is located at the dwarf camp.
There will be a dwarf, Thorgel, in there. You will argue about how you each got in there. You will find out the dwarf is from the outpost at the bottom of the Underground Pass! He will give you an item list consisting of 50 items. If you give him all of the items, he will give you a death talisman.
It is highly recommended to just buy a Death Talisman from the Grand Exchange, as they are extremely inexpensive. Enter the Death Altar and use your newly made crystal on it. It will start to glow.
Exit the death altar, then return to the black crystal. Use the newly made crystal on the black crystal. It will change colors and reactivate the temple's safeguards. Return to Arianwyn and tell him the news. He will girve you a crystal trinket to allow you to enter through the temple's front door.