A few terrain suggestions:
-Temples! Whenever someone builds a temple of notable size, there should be a little marker added onto the map. In my case, the only map-worthy temple is the giant coral spire at 20.11, but that may change. This also goes for the three Praeclusium entrances as well, I imagine, and big cities like Odreploy.
-Trenches! Specifically, one extending from 11.14 to 05.06 or so. Similar to the marianas trench. This can be full of whatever exotic lifeforms you want, feeding off of chemicals, magma or even magic.
-The island centered on 15.17 appears to be a jungle of sorts. I recomend it being full of giant bamboo, giant bees that nest inside giant bamboo stalks and giant spiders that eat giant bees. Likewise with the similarly jungle-ish area around 20.15, except maybe a little lest giant-sized.
-The rest of the big southern island is a desert of sorts, it looks like. I'm not really sure what should be there. Maybe micelus's jagged rocks idea, that does admittedly sound pretty cool. Maybe make the whole island like that, but with trees poking out from between the rocks in the more forested parts.
Locations of Note:
17.09: First mioxed Retha-Calx settlement.
20.14: First landfall on southern isles.
20.11: First Temple of Niklas
Other Questions/Comments:
@Wimdit: How much EE do we get this turn?
@Sinpwn: How could the Calx enter the Praeclusium legitimately? I'm hoping you're not wanting writing or fire or something to get in, since the Calx have absolutely no use for writing and live under water, after all.
@mcclay: I'm personally partial to the mixed civilization idea, to be honest. I can't really find a legit excuse for the Calx to even notice the Retha yet, let alone attack them.