In a world of MMORPGs where grinding is the name of the game, the whole concept of a "hidden quest" doesn't make a lot of sense. It's hard to find in the first place which defeats the purpose of streamlining the leveling process, is not exactly XP rich, so why bother looking for them, never mind completing them?
Back in the day, when World of Warcraft was first released, there were more secret quests hidden throughout Azeroth. These are the kinds of quests that are only available in isolated locations, found when picking up certain items, or only appear under special circumstances.
6 Dark Iron Legacy
Not exactly a secret, because everyone dies in Blackrock Depths and has to run back through the Tomb eventually, but few characters actually complete the chain that starts with Dark Iron Legacy. Players can only see the ghost of Franclorn Forgewright and pick up the quest he offers when they're in ghost form, which is one advantage of the long run back.
The player gets a hammer, Ironfel, and the ghostly dwarf instruct the player to complete the statue of himself in a monument inside the dungeon. The reward for completing this is the Shadowforge Key, which not only grants easier access to the bowels of the dungeons but is also required for one of the Achievements, The Keymaster.
Forgewright is a famous person in WoW lore, which makes this quest line more interesting if the player knows some history. The name is better known on the Alliance side where he's the designer of the Stonewrought Dam in Dun Morogh, an awesome structure that most Horde players never even notice.
5 Spawn Of Jubjub
While the character is exploring BRD, they can stop by the Grim Guzzler and buy a few Dark Iron Ale Mugs. This is the only place in the game where they can be found and make sure the character has at least two of them because they're needed to unlock another hidden quest. Not only does Spawn of Jubjub require at least two frothing mugs of ale but also the presence of the Darkmoon Faire, so players that have timed this badly might need to wait a couple of weeks.
When the fair appears in Elwynn Forest or Mulgore, go and find an NPC named Morja. Place a Dark Iron Mug at her feet. After a few moments, her pet frog Jub Jub will hop over and take a drink.
This is when she offers the player a quest called Unhatched Jubling Egg and all that's needed to complete it is to give Morja the other mug of Dark Iron Ale. The reward is an Unhatched Jubling Egg that sits in the player's inventory for a week before hatching into a non-combat frog pet.
4 CLUCK!
Not as many Horde players get to finish this quest, simply because chickens are harder to find compared to the Alliance side, but there are a few in the Barrens and Tarren Mill. CLUCK! Is one of the classic hidden quests and it's available to both factions but more Alliance players find it and complete it.
All the character needs is some Special Chicken Feed, which is available from Farmer Saldean for Alliance players and the Auction House for Hordies. Start by finding a regular domesticated chicken and do the /cluck emote to it several times.
After a while, the chicken looks up at prompts the player to inspect it. It offers a quest named "CLUCK!" And spells the name of the NPC that sells chicken feed. After the player feeds the chicken they are rewarded with a Chicken Egg that hatches into a non-combat pet.
3 The Essence Of Eranikus
One of the infamous unfinished quests of Classic WoW, this chain seems to get another piece added with every expansion. The quest is only available if the player has picked up an item called the Chained Essence of Eranikus while they were exploring the nearby Sunken Temple.
The item has an interesting history. It's connected to the Green Dragonflight and the Emerald Dream, and a fan theory says this hidden quest was part of old plans for an Emerald Dream raid that were never finished. If the player has it, they can take it to a mysterious elf named Itharius, who's hidden in a cave in the southwestern corner of the Swamp of Sorrows. He tells an interesting story about Ysera before sending the player to another NPC in Wintersrping.
The quest ends in that northern zone, but on a cliffhanger with Umbranse the Spirit-Seeker, an auger with the talent of speaking to the dead. However, the tool he uses to spirit-seek has gone missing and he has nothing more to say on the matter.
2 Cortello's Riddle
It's just a little scroll, sitting on the deck of a ship, it could be anything, why even bother with it, assuming the player even notices it? However, curious gamers will click on this scroll and find it starts a quest called Cortello's Riddle which sends them to various locations throughout Azeroth in search of treasure.
The quest line leads to the Swamp of Sorrows, Dustwallow Marsh, and finally the Hinterlands. The reward is a worthy one, a 14-slot bag, which is one of the greatest things a character can get at this level
1 Message In A Bottle
There are all kinds of things that a beachcomber can find along the shore, and if a player keeps their eyes peeled, they'll see a bottle submerged in the sand. In fact, they'll see several, and not all of them start this quest. Some of them just contain sad stories of thieves, pirates, and slaves that met their final, unhappy end in Stranglethorn Vale.
There's one bottle, however, that contains a note from a lost princess that starts a quest called Message In A Bottle. Her name is Poobah, and she's being held captive by a giant gorilla named King Mukla. Slay him, free her, and get some decent mail bracers with a generous Stamina buff as a reward. And if anyone is thinking that this is a King Kong reference, they're probably right.
World of Warcraft is currently available on PC.