WoW Classic, Infinite Respawn Farm, Low-Level 11-23, Horde Preferred (Patreon)

The quest "Counterattack!" https://classic.wowhead.com/quest=4021/counterattack , obtainable from Regthar Deathgate, west of the Crossroads and north of Wailing Caverns, in the Barrens, has an unusual feature.

When you start the quest you should spawn a large Kolkar army (speak to Rethgar if this isn't happening). The quest requires you to kill a warlord, but you don't have to go anywhere near the warlord and can just kill Kolkars with the aid of the orc npc's.  The Kolkar mobs are normal npc's and award full experience. 

There were too many mobs for me to even come close to killing them all, but the mobs are in any case instant respawn. Caution is advised: it is quite easy to get overrun. This is by far the best place to grind at this level if you can survive it. 

In addition to experience, this is not actually a bad place to farm gold: at max level you can kill the mobs fast enough to make 30G + an hour-the main difficulty is because you are getting a high frequency of low-level drops your bags fill up too quickly.  You will also need add-ons to speed up the looting process. 

Alliance players can grind these mobs but they can't trigger the quest, so they are reliant on Horde players to do so for them. The Kolkar disappears after a while only to return when another player triggers the quest.