Gjalerhorn is a small area in the North of the Howling Fjord.
No quest asks you to go there; it has no specific use except puting some flavour to the game.
Since absolutely no one ever bothered about this location, a massive bug went undiscovered for years.
The problem with this place actually comes for its mine.
The building is the same WMO as the mine from Arathi Basin.
There are some snobolds around in the area. Yet if you decide to enter the mine they will suddenly disappear.
In fact the game considers that you're not into the Howling fjord anymore but into a battleground.
In this place you'll be able to use items that should only be used for PvP and not in the outside world.
The most useful thing I found was a way to increase your maximum health through food.
This bonus will then be preserved anywhere you go unlike it should.
Finally, note that this place follows battlegrounds behaviors which can lead to weird things :
If you happen to die there, your ghost will not be ported into a graveyard but simply spawn on your own body.