Education quest: Where's the horn?
 

I've completed both areas in Guttorm's cave. I cannot find the horn in the Cyclops cave. I found a bunch of stuff but no horn. I have canvassed every square and there are no more places to dig. Sigh.

Try going through the area slowly so you see the beam of light easier (sometimes I run past them too fast) and try to hug the wall as much as possible because sometimes the chests are buried in the tiniest of places.

You can also keep pressing (not hold down) "D" constantly as you wander around, but from your post it seems you might already have.

EDIT: The horn is actually NOT in the area where you find the cyclops but in another area to the east from Guttorm.