...How is this a Spoiler? All it says is 'Can't find cave' anyone who has even downloaded Dawnguard and talked to a single Guard will know what this cave is.
No offense Bootysweat but you've been moving a lot of non-spoiler threads to the Spoiler section recently...
You are asking where to find some cave to start a quest.
The answer to your question is a spoiler. Do not post spoiler threads in the General section. They go in the Dawnguard Cheats, Hints and Spoilers section.