Underdepths

Background
A separate realm full of strange and dangerous things that exists deep under the Oceans of Foundation. Very few people have successfully travelled directly to the Underdepths by braving the depths of the Oceans, but there have been Shrouds discovered that have linked to various places in the Underdepths, which implies that this location is in a different realm than Foundation is. If this is true, this is the only known realm that is accessible by a means other than travelling through a Shroud.