Seeing that a certain quest rewarded horse was "invincible," and I was being lazy, I took a shortcut off of a mountain with a leap of horsey faith.
Splat.
My character hit the ground, as well as my horse. Though I didn't see where my horse went, it looked like he went through the ground. Amazingly, I got up after I thought I was dead, found a Daedric shrine. Proceeded to do the quest, of course!
I found my horse 30 minutes later, slumped against a tree.

BUT I GOT A COOL DAGGER!