Ok, here's a recap of your doings so far inside the Cairn. Not in chronological order, but easier to follow this way. Follow along on the last map I provided in the IC section.
You searched the alcoves in the southern half of the map and found the following:
Bottom Left - Child's bedroll
Bottom Right - Nothing
Middle Left - Broken thing-a-ma-bob, with arcane runes for transportation
Middle Right - Collapsed
Top Left - Fresco painting showing the room to the north with lanterns in the following order Red, Orange, Yellow, Green, Blue, Indigo, Violet
Top Right - Partially collapsed, but found the wolves den, where serenity found an indigo lantern and an elvish arm band.
You fought and killed the wolves that were using the Top Right alcove as a den.
In the northern section, You've found a room excatly like that depicted in the Fresco, except that the red and indigo lanterns are missing. There is also a sarcophagus in the center of the room. You should go back and read the initial description of the sarcophagus and the room itself for more detail. The green lantern was lit by an everburning torch, which Mohan has removed and is carrying with him.