This achievement is unlocked once you have cleared all caves and striking locales in Coldharbour and unlocked the in game 'Coldharbour Master Explorer' achievement.
To reach Coldharbour you must complete the primary alliance quest line. Once you have completed the final alliance quest you will be given a new main quest which will lead to Coldharbour.
A 'cleared' cave/locale will show up on your map as white.
You only have to clear striking locales and caves (not any other area such as towns/dungeons).
If you go to your menu, journal, achievements, then exploration you go almost all the way to the bottom to the Coldharbour section wherein you may see the "Coldharbour Cave Delver" and "Coldharbour Pathfinder" to see how much progress you have towards the achievement in that area.
Striking locales:Striking Locales show up on the map as an eye.
Simply enter the area where the eye is and it should discover it. This classes it as being cleared.
Caves:Caves show up on the map as a tilted torch.
Caves often have a quest in them, but this is not necessary to complete for the area to be 'cleared'. Instead you can ignore it and just travel through the cave until you reach its boss. The cave boss will have the special heath bar and a unique name. Once you have defeated the boss you should get an in game achievement and the cave should be classed as cleared.
Some caves in Coldharbour can be misleading when looking at the area map because there are multiple levels, so if you can't seem to find the boss then look for some way to go to a higher level.
Map:This map shows the completed Coldharbour map. Use it to find the locations of the caves and striking locales. Note that the northern striking locales will require progress in the main quest in order to enter the area.
http://www.gamemapscout.com/tes-online/coldharbour.htmlCredit for the map goes to www.gamemapscout.com.