As of 07/19/2010 Confirmed Not Working. I tried on three different occassions. (Broken)
As of 4/4/2010, this achievement is not unlocking.
It can be achieved by stepping into the pool at the innermost part of the Emlyria Caverns (in Chrace), the entrance to which is at (12.8k, 23.1k). Enter this cave from the North.