After choosing to forge ahead to see the Unseen Elder, you can choose to head out or say you need more time. If you choose to go now, Regis will join you on the boat and converse for a bit, otherwise choosing the latter means to go without Regis' comments. However you get there, follow the steps around to where Regis is now waiting at the sealed door and interact with it to reveal the entrance, then head inside.
You'll eventually come across a split where a submerged path and an upper path are. Both lead to the same room eventually, but if you want Regis' help, take the dry path until you come across a fleder. Once killed, you'll notice there's 3 paths off the room: the one you used to get there, one with a lit torch, and then another one with a ledge. If you do a running jump you can easily get over it to find some loot, including in the chest the Hen Gaidth gauntlets and steel sword (if you took the water tunnel, this is where it'd have come out).
Back in the fleder room, take the path marked by the torch until you reach the next room and a cutscene will start. Note: drinking Black Blood before this has no effect on the Elder. No matter what you say it's clear the Unseen Elder isn't accepting visitors and tosses Geralt into another part of the cave. Important: Once you've regained movement, be sure to look behind you to pick up the two swords you had equipped (and fell off).
Around the stone column is your health potion. Pick it up and drink it and Geralt will pass out and then come to, this time with full health and movement once more. Depending on what all you had on you, you may have quite a bit of items you lost in your fall. Before the next ledge is typically your crossbow and bolts as well as a small item, likely your other healing potion. If you didn't already, pick up your swords on the other end and that should be all your lost items.
Escape the cave
Now, head up the ledge to find a highly unusual room where water moves in very odd directions. Jump down for Geralt to comment about the other ledge, then go to the campfire and pick up the Mage's notes. You can examine the nearest waterfall for Geralt to comment on it, but otherwise look and examine the footprints near the campfire and follow them to the left side of the main chamber. Note that the path will split just before the next room. The path up the ledge goes to a dead end room with 3 protofleders, a unique vampire to this cave system, but more importantly the room contains a chest with the Hen Gaidth mask and trousers.
Continuing along the main path into the next room you'll run into 2 protofleders (your first if you didn't go up the previous path). The footprints pick up again on the other side and continue up the ledge. Follow across the bridge until you find an old megascope to examine and a second mage's notes to read. Continue following the path to a stream flowing upwards and you find yourself this time walking upside down on the ceiling part of the cave. Right in front of you, against the wall, is another chest, this time with the final pieces of the Hen Gaidth set: the armor and boots.
Follow the path until you get to a gap between you and a protofleder. If you stand behind the roof outcropping, near the corner in the path, you'll see to your left (the center of the room) a ledge you can jump to. However, you need to find something to appease the Elder, so jump across the other gap to fight the protofleder and search the mage's body for a crumpled letter and read it. Also, the unique silver sword, Cantata, is next to the mage's body. Now, turn back to the gap you jumped over and pick up the rose-colored stone next to it, the peace offering you need to show the Elder, then jump over and use the previous mentioned gap to jump over to the middle platform. Head around until Geralt remarks on the large stone before you. As you might have guessed, use Aard on the base and it'll float "upwards" creating the needed step on the bottom of the cave to reach the other side, then turn around and jump into the large "upward" flowing waterfall and you'll end up back near the campfire.
Speak to the Unseen Elder
Now climb up onto the previously unreachable ledge and make your way out of the cave and eventually returning to the main chamber with the Unseen Elder and an immobile Regis. He'll accept the offer and then you can talk to him. However, note two things:
- Do NOT ask more than one side conversation. He will give a warning not to waste his time with the first one and if asked a second, he will instantly kill Geralt, requiring one to load a previous save.
- The second time you must choose out of 3 options, the only correct choice is the third ("Dettlaff spells trouble for you"). Answering incorrectly twice (the 1st and 2nd options) will again, lead to him instantly killing Geralt and having to load a previous save.
Afterwards, you can choose what to say and he'll agree to force Dettlaff to meet you at Tesham Mutna Ruins. Once outside, you can talk with Regis a bit before heading off to the meeting point.
- Geralt now knew how to find the Unseen Elder's lair. He went to fetch Regis, and together they set off to meet the ancient bloodsucker. I can only imagine how difficult a[sic] Regis' predicament was. After all, he was about to help his dear friend set a deadly trap for another of his close comrades...
- Regis had expressed some concerns about meeting with the Unseen Elder. These proved not at all unfounded nor in any way exaggerated. To say the ancient vampire treated his guests impolitely would be a gross understatement. In a matter of moments, the Unseen paralyzed Regis, while he took Geralt and, much as if he were a rag doll, hurled him to the floor of the cave. The witcher was hurt rather badly. Yet somehow he needed to find an understanding with the vampire...
- The Unseen's ghastly reputation proved entirely deserved. He had exactly no tolerance for unexpected guests. And he was mortal danger embodied. In the end Geralt managed to convince the creature to help him, but persuading the beast had almost cost the witcher his life. I have no doubt the witcher breathed a sigh of relief after their meeting, and drew comfort from the thought it would not be the Unseen he would face during the final confrontation at Tesham Mutna.
- Go to the Unseen Elder's lair.
- Open the entrance to the Unseen Elder using Orianna's key.
- Enter the Unseen Elder's lair.
- Find a healing potion.
- Drink a health potion to regenerate Vitality.
- Get out of the cave.
- [Optional] Collect the items and gear you lost as you fell.
- Find a way to appease the Unseen Elder.
- Find a way to get to the exit.
- Read the mage's notes.
- Find the mage.
- Search the body.
- Find an offering for the Unseen Elder.
- Destroy the wall using the Aard sign.
- Jump into the water.
- Reach the platform and get out of the cave.
- Talk to the Unseen Elder.
- There's a wall mural on the left as you enter the cave which appears to be a direct reference to reliefs of the Sumerian god, Anunnaki.