Explore Icecrown

Or for TomTom users

/way 73 29 Sindragosas_Fall
/way 45 16 Shadow_Vault
/way 35 36 Jotunheim
/way 33 29 Valhalas
/way 11 50 Onslaught_Harbor
/way 30 63 Fleshwerks
/way 41 68 Corprethar_Horror_Gate
/way 44 64 Conflagration
/way 51 59 Ymirheim

and ...

/way 52 47 Aldurthar_Desolation_Gate
/way 78 59 Scourgeholm
/way 62 40 Bombardment
/way 53 89 Icecrown_Citadel
/way 68 65 The_Broken_Front
/way 83 73 Valley_of_Echoes

Onslaught Harbor discovered at 11, 51.

Because I couldn't find a comprehensive list of coordinates for the locations on this achievement, I decided to undertake the daunting task, lol! Keep in mind I did this on a flying mount and so if you don't have the flying mount things could be a lot more difficult for you. I also took coordinates down from TomTom basically when it said I had discovered the area. Here are the coords I got:

73 29 Sindragosa's Fall
45 16 Shadow Vault
35 36 Jotunheim
33 29 Valhalas
11 50 Onslaught Harbor
30 63 Fleshwerks
41 68 Corp'rethar: The Horror Gate
44 64 Conflagration
51 59 Ymirheim
52 47 Aldur'thar: The Desolation Gate
78 59 Scourgeholm
62 40 Bombardment
53 89 Icecrown Citadel
60 65 The Broken Front
79 68 Valley of Echoes

Good Luck!

p.s. There is a link to the map on Greyhame's post if you want a visual.