Mulgore cave

An unnamed cave can be found in the northeast corner of Mulgore, near the top of the mountain, while taking the flight path between Orgrimmar and Thunder Bluff. This area consists of a tauren hut and a cave, both of which were completely empty.

As of Battle for Azeroth, the hut was taken over by Verd Twiceswindle and Venture Lackeys.

Getting there
The only way up there was very hard to climb, and if you were not specifically lucky, it could take more than an hour to jump the thin ledge. However, after patch 3.2, it's possible to take the The Zephyr between the two cities and jump off onto the top of that mountain. As of Cataclysm, you can simply fly there.