As requested, spoilers abound...
d20fool said:
What is Whitehearth and where is it and what is going on there?
It's a house Cannith research facility. It's underground, hidden in what appears to be a mine shaft. It has a couple of levels with central hub rooms that rotate with the right keys to give access to different areas. It was used for various experiments and is currently inhabited by some of the results/survivors such as living spells, awakened animals, constructs, and elementals. Some items affiliated with the schema in
The Forgotten Forge can be found there.
As for what else is going on in the Mournland in the module, there are some battlefields with eternally fresh dead, one of which is inhabited by a carcass crab (from the Eberron campaign setting).
There's also a village just on the Darguun side of the border but which would fit right in on the Mournaland side. It's filled with once molten, now solidified glass which trapped the inhabitants like the ashes of Vesuvius did in Pompeii. There are some agents of the Emerald Claw there trying to discover where Whiteheath is (using a map room a la
Raiders of the Lost Ark), and they've animated some of the villagers remains as glass coated zombies.