How to reach Thalassius, the Coral Keep
In order to reach Thalassius, the Coral Keep you'll first want to take the Guild Hall portal to Katta Castrum. Once you arrive here, travel south through the zone until you go through the second set of double doors. From there, head east and north until you reach Thalassius, the Coral Keep - shown on my map above.
Also, you might just be able to go east out of Katta Castrum to get to this place, for some reason though I remember it being blocked off, which is why I always go south out of the central area. I might just be retarded though - so if you try it yourself let me know with a comment below!