This dream crystal is among the several crystals found in the queen harpy's lair.
When Geralt loads this dream crystal into the viewer, he sees a dream belonging to Iorveth.
- A discussion on the Official Forum suggests that Iorveth's dream amounts to the elf basically being stoned and having the munchies. The rough translation would be:
Oh, carrot, tasty carrot,
With even fat/lard on top,
And also chicken with parsley...
- Another interpretation is that he dreams of living in peace and quiet with an abundance of food and drink. Which explains why he is talking about the excess of food. He's probably a little high too though.