Sedna Abyss, also known as Sedna Trench, is an infamous location in the seas between the Skellige islands and Cape Peixe de Mar and tends to be avoided by the islanders as ships disappear in this area due to unnatural causes. In particular, if entered, a maelstrom forms out of nowhere and the unlucky ship disappears.
It's later revealed the islanders were right about it being unnatural. Unbeknownst to most, the mage Vilgefortz created the magical maelstrom here, using it to teleport any ships that enter it away to one of his hideouts in faraway Ebbing, where the ship and most (if not all) the crew die on crashing into land. At one point in the 1250s, he worked with Emhyr to try and bring him, his wife Pavetta, and their young daughter Ciri to Nilfgaard while making it look like the family perished at sea by using this maelstrom, but the plan went awry and only Emhyr was teleported away.
In 1267, Yennefer, in her pursuit to find Ciri, learned that during the Thanedd coup someone had teleported to a point right in the middle of the abyss with the assumption they knew a ship was going to be waiting for them there. Theorizing it was someone that took Ciri or likely knew what happened to her, Yennefer sailed into the abyss on the last day of August and, sensing it was her, Vilgefortz activated the maelstrom once more to capture the sorceress.
- This fictional location shares the name with the Inuit goddess Sedna.