The easy way to instances! Quests include both Alliance AND Horde, some of which may be duplicates. (I filtered some out but may have gotten caught by others ^^)
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Eastern Kingdoms:
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Stormwind Stockades - Levels 15-20
Found in Stormwind, North West part of the mage district on the OUTER ring. Not as easy as Ragefire Chasm, but pretty short... if not shorter with a good group. I dont agree with the level range given, but I would say its around 20-24, I dont have to much experience here, but I know theres a few bosses, very short, and you can get fairly fast experience here with a good group.
Quests - Roughly 8
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The Deadmines - Levels 20-25
Found in Westfall on the southwest coast in a town. Lower level instance, with not very many elites until you get towards the end, best to normally take levels 18-23 so that you can get the best experience possible, and be able to get through alive. The one bad thing about this instance is that its not complicated at all, and almost a straight path to the bosses until the end, which you still cant get lost on. In my experiences, this is probably easier then Wailing Caverns at some parts, but harder in others. Make sure you have a group that knows what they are doing.
Quests - Roughly 6
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Shadowfang Keep - Levels 20-30
Found on the west coast of Silverpine Forest, just south of the mountains. Very easy instance with a good group. There are no confusing twists or turns, but maybe 1 or 2 decisions to make throughout the way. All of which will still take you past, or to the same bosses. Recommendede levels would have to be 24-28, keep in mind the last boss does cast, and does like to hit hard at times, as well as teleporting around so its harder to take him on, make sure to have a caster or someone who likes to jump around.
Quests - Roughly 5
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Gnomeregan - Levels 25-35
Found on the west side of Dun Morogh in the mountains. This is a very hard instance, if not one of the most intense for its level range. The only reason to really go there would be for good experience (You would be better off in Scarlet Monastery doing fast runs) or the lovely legs that a quest gives here (
http://wow.allakhazam.com/db/item.html?witem=9624). I would recommend levels 28-33 because it gets very intense.
Quests - Roughly 13
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Scarlet Monastery - Levels 30-40
Found north of the Undercity in Tirisfal Glades. Very easy to get to and maintain on anything but PvP if you are Alliance. However, on a PvP server its best to get into the instance and wait for a party, unless of course you have a high level with you. The horde dominate this instance, and love to PvP while you wait for incoming party members. Overall there are 4 sides to it.
Graveyard - Easiest of them all, recommended levels 32-35
Library - Easy overall, recommended levels 35-37
Armory - Easy with a good group but longest, recommended levels 37-40
Cathedral - Hardest, recommended levels 37-42
Quests - Roughly 8
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Uldaman - Levels 40-50
Found at the south entrance to Loch Modan. Very easy instance if you have a group that knows what they are doing (of course). I dont know much about this instance other then the final boss is a pain, most groups never finish him or even try because of how hard the fight is. Whether hes pounding you down, your healers running out of mana, or he summons his friends to fight by his side, the whole fight is a pain, and in my opinion a waste, other then the quest you get afterwards of course, make sure not to skip it. Recommended Levels - 38-45 if you want to get the last boss down, raise the requirements up to 40-46 for a hopeful guarantee.
Quests - Roughly 17
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The Temple of Atal'Hakkar (Sunken Temple) - Levels 50-55
Found in the water in the east part of the Swamp of Sorrows. This is by far one of the longest instances in the game. The instance isnt hard after one run of someone showing you how to do it. But it is very long, not even hard at all, unless you do the bottom part of the instance, which many skip. The whole thing is overall a long instance and I recommend going for your level 50 quest and getting it over with. The instance has good experience waiting if you want to spend time, but its a continuous boring grind.
Quests - Roughly 17
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Black Rock Depths - Levels 50-55
Found in Blackrock Mountains. Another fairly long instance with about 21 parts to it. The instance is usually broken into parts. Whether your going for the last boss, Molten Core attunement, or going to the arena to farm, its not always hard. A few parts of the instance may require you to be level 60, and others may require you to be only 52 (my recommendations), It all depends on how well you know the place. I personally do this for only a few quests, one of which being attunement, and then I am out. I dont have many recommendations other then 54-60 depending on where you are going.
Quests - Roughly 37
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Scholomance - Levels 57-60
Found in the North part of the Western Plaguelands. This is a fairly easy instance if you have an experienced group that is serious about the game, and dont like to mess around. The level requirement in my book is 58-60, with the occasional 57 being a healer and nothing more. The instance is overall straight through and most people know what they are doing.
Quests - Roughly 20
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Stratholme - Levels 58-60
Found in the northern edge of the Eastern Plaguelands. There are two parts, Undead Strat, and Live. The live side I find very good for farming because you could make some fairly nice money (atleast pre-bc), and the undead side could drop you some nice armor drops if you didnt want to raid. My suggested levels would have to be 58-60.
Quests - Roughly 19
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Blackrock Spire - Levels 58-60
Found in Blackrock Mountains. I would suggest a high level group, you can do 58-60, but always try to get as many 60's as possible because its easier, and you have a better chance of finishing. There are different ways to go through the instance, but UBRS (Upper Blackrock Spire) Is of course, above LBRS (Lower Blackrock Spire) But they are in the same instance. If you plan on doing both, be sure your group is okay with it, I would recommend doing them on different days because they arnt always short. Keep in mind, some of the bosses are very hard and unforgiving.
Quests - Roughly 30
Thanks for reading, I hope this helped, Keep in mind I never did the high level instances to much, I mainly did them either to farm a couple times or not. I have done atleast each of these instances once, but never enough to memorize the complete layout. I ended up stopping the high level instances to end game raid with my guild back before pre-bc and never needed to go back.