The Sightless Sea is by far the largest of the known vaults of Orv. It lies beneath the Arcadian Ocean, and is of a similar size. There are numerous tiny islands in the sea, many settled by urdefhan but others claimed by even stranger creatures. On average, the sea is a mile deep, but in places it is much deeper.
The Sightless Sea is linked to the Arcadian Ocean via the “reverse waterspout” known as the Braid, which leads up to the Inverted Sea. A current from the Sightless Sea flows up the Braid, through the Inverted Sea, into the Arcadian Ocean and then into the Inner Sea. From there it seeps down into Lake Nirthran and eventually finds its way back into the Sightless Sea. In theory this grants the aboleth access to most of Golarion, although there have never been any confirmed sightings of aboleth coming down with the rain that lands in the Midnight Mountains.
The aboleth are the most powerful faction in the Sightless Sea. At one time they ruled it all, but today they are apparently content with just controlling most of the depths. Other foul creatures live in the deep regions outside of aboleth territory; the shoggoth are perhaps the worst, and may even pre-date the aboleth.
Some of the islands are inhabited by urdefhan outposts, while others are populated by genies, neothelids, dragons, exiled fiends, and groups of technologically advanced skum. The sea itself is plied by ships piloted by denizens of Leng, tieflings, telepathic munavris clad in jade armor, and even more unusual creatures. Munavris primarily use their naval skills to fight the urdefhan.
- James Jacobs and Greg A. Vaughan. (2008). Into the Darklands, p. 53. Paizo Publishing, LLC. ISBN 978-1-60125-140-4
- James Jacobs et al. (2011). The Inner Sea World Guide, p. 61. Paizo Publishing, LLC. ISBN 978-1-60125-269-2
- Josh Colon et al. (2015). Occult Bestiary, p. 34. Paizo Inc. ISBN 978-1-60125-767-3