Searched for a good 15 minutes, there no quest at the quest marker. Maybe I just missed it, but was standing on the marker for 5 minutes. Tried getting to it from the outside and you can't climb the mountains.

Edit: I just got the quest Bitter Rivals (https://www.wowhead.com/quest=310/bitter-rivals), and it appears to be on the same marker as Guarded Thunder Ale Barrel, possibly the start marker is wrong?

Just to confirm, you saw the quest to get the Guarded Thunder Ale Barrel but you didn't have the quest for Bitter Rivals yet? I know this quest makes you buy the thunder ale for the dwarf in the inn's basement and he walks away. then you interact with the barrel behind him but in-game there is no quest marker on the barrel itself. you have to mouse over it and it highlights then you can interact with that quest.

Yep. I walked into town and started picking up quests, couldn't get that one. Didn't realize what it was until I was completing Bitter Rivals, and then I put two and two together.