NO.10 Escape from Coilskar Cistern
Escort Earthmender Wilda out of Coilskar Cistern and then seek out Earthmender Torlok at the Altar of Damnation, found at the western outskirts of the Hand of Gul'dan.
Strictly speaking, this quest is not so concealed. To the north side of Shadowmoon Valley, Coilskar Cistern is not connected by any other quests. Therefore, in addition to those people who want to farm shadow pearl, Cobra scales or miners who want to make WOW gold, few people come. The NPC of the quest is hardly known and Concealed, so that put it into the list as the most hidden quests is reasonable.
Hidden index: 60%
NO.9 Thrall, Son of Durotan
Venture to Orgrimmar and deliver Geyah's message to Thrall.
I believe many people have heard about this quest, Horde side is already known through various channels and complete it and make World of Warcraft gold. But in the very beginning of the expansion, few people know. This quest is at a small house in Nagrand Spring sentry. Start from a convoy quest by a NPC. Complete the convoy quest. Complete a series quests that Blademaster in Burning Blade Ruins assigned to you. Complete the elite series quests assigned by northwestern demon hunter. Then you will be leaded to the quest of "visiting grandma", doing the quest step by step until Thrall back home.
Hidden index: 65%
NO.8 Need for a Cure
Find Kor'ghan in Orgrimmar and get the Venomtail Antidote. Then bring the antidote to Rhinag near the northwestern border of Durotar. You have to complete this quest and earn some WOW money within 45 minutes.
Hidden index: 75%
NO.7 Dark Iron Legacy
Slay Fineous Darkvire and recover the great hammer, Ironfel. Take Ironfel to the Shrine of Thaurissan and place it on the statue of Franclorn Forgewright. Do you know how to get the key to Blackrock Depths?
Hidden index: 75%
NO.6 MacKreel's Moonshine
Take MacKreel's Moonshine to Brewmeister Bilger in Southshore. Complete this quest and make some WOW gold and buy items and mounts you want. Had quite a bit of the ol' Moonshine last night! Longbraid would have my head if he knew that I passed out during my watch. The noggin hurts something fierce. Felt as though a whole brigade of siege engines passed overhead, all that rumbling. Oh my, look at the time! I promised Brewmeister Bilger in Southshore that I'd repay my debt to him by sending some Moonshine. But there are just 15 minutes left before I'm overdue!
Hidden index: 77%