The Headless Hunt, I Need Help

Hello,
I am doing the quest "The Headless Hunt" but i am having problems. I am on the final step when i have to destroy the lost spirits (according to my quest book). I have done that three times now, but i could not find a way out so i /kill'ed. When i go back to the quest NPC it says: "you should check your questbook to find out what to do" or something like that.

My guess is that by /kill'ing i skipped a step. So my question is: "How do i get out from where the Lost Spirits are?"

EDIT: Also for anyone interested i found a Herobrine easter egg in there ;)

 

Behind the Lost Spirits is a TP region that tps you outta the cave.

 

Didn't see that XD stupid me.
Will go do it now.
Thanks ;D