Open the second level of the tomb of the king under the mountain.
Start at the end of Erebor: Opening Thrain's Tomb.
Head down into the tomb, then examine the carving of Thrain carefully. Once you have continued past the statue, head into the chapel. Now you will need to locate a gem in one of the rooms around here, once you have located the gem you will have to find a room, which when lit to be the same colour as the gem, allows you to place the gem into the mural somewhere. You will know when you have completed this as you will hear a grinding noise and a new exit will appear in the chapel.
As there are several freebies in the next area, often this quest has already been completed and you can simply keep the gem you find.
In the room with the carving of Thrain you can get a necklace by searching the lid of the sarcophagus and a ring by searching the sarcophagus.
You can also potentially complete Erebor: Dragon Cutter here.
do d,push axe,push eyes,n
You now need to find the gem, there are several items randomly dotted around the rooms off of the chapel (chest, bookstand, cabinet, prie-dieu and bench), when you try to get these items they will crumble and leave some debris. When you search this depris you will wither find A black widow spider, a splinter or a gem. You are looking for the gem.
When you have the gem you will need to light each room off the chapel the same colour as the gem you have by lighting/extinguishing the candles.
For A red gem:
do extinguish blue candle,extinguish green candle,light red candle
For A yellow gem:
do extinguish blue candle,light green candle,light red candle
For A magenta gem:
do light blue candle,extinguish green candle,light red candle
For A white gem:
do light blue candle,light green candle,light red candle
For A green gem:
do extinguish blue candle,light green candle,extinguish red candle
For a cyan gem:
do light blue candle,light green candle,extinguish red candle
For A blue gem:
do light blue candle,extinguish green candle,extinguish red candle
Once you have lit the room correctly you will need to
insert gem into eye
If it does not work, move onto the next room and repeat until it does work.
If any of the information here is missing, or wrong, please let us know.