Have gotten Anephas back, got out of his tomb,went all over the second sea, found Cet's tomb, but can't find Collasium?? Also must have missed Pirate treasure in Kerah's room, but block is not moving and I can't get back there. I must have done something really stupid here. Spoil me please. TIA

Collasium is an underwater city. Do you have your "scuba gear" ?? The city lies east of a small clearing on the west shore of the Lost Sea. (on the map probably right under the word "uncharted")
Once you've seen and talked to Kerah and exited that area, you cannot return there via the pillar in the temple. You really shouldn't need to go back there.

So did I spoil you???

Wyv