This achievement is part of the storyline and unlocks during chapter 4 with normal progression. You will have to talk to the ice chief and he will ask you to build a tower for the dragon. After that you will have to talk to him again. There will be a little cutscene and right after you should unlock the achievement.
Note: This achievement seems to be buggy after talking with a few people. Ariose999's advice is to save manually when you get to the ice kingdom for the second time(when going for metal) and that way if it doesnt unlock you can easily restart from there and hope it does.
Update 5/5/11**: cloud2795 and Doomed Satsuma have told me they received it a little later on in the story.
cloud2795 said :Just to let everyone know I got the achievement at the same time I got the Reunited (And It Feels So Good).
Doomed Satsuma said: I didn't get it until I'd started a new game and played right up to the part where you smash the 3rd helper out of the puppy dreams thing you have to get for the witch.
So if you don't get it normally like I did early on, you may need to wait later on in the story like cloud2795 and Doomed Satsuma or just try Ariose999s' solution.
Hope this helps everyone out!