I think that Lenos is asking a more basic question.
Lenos, when you get to the plateau level, you want to run around smashing gravestones. Sometimes these release monsters, which you kill or ignore as you like. Sometimes they release lost souls, which look like blue balls. Kill the lost souls. Then you get rewarded with sigils.
What's interesting is that there are also "puzzles" to solve. For example, find fire and find water, and use the water to put out the fire, and you can get a reward of many sigils. Read the threads on this forum, for more clues to puzzles.
Elite Difficulty and get all the tombstones. The best strategy that I've found is that you get a party together and rush to the top left corner. From there, go from side to side in a thorough pattern to get all the tombstones.
They did nerf the payout and the chance to find lost souls.