I think Crater can be both on land and under seas. Not 100% sure. I've found it a couple times. Just like the Glowing Hill. Actualy, I remember the esoteric and mysterious times of Dom 1 & 2 when The Glowing Hill would allow you to recruit Vans...
That one Death site that lets you to summon Wights (or was it Banes, as units...) is also rather kickass.