Cannot reach the Ancient's Nest

After speaking with Morrigan at the end of the Regrets of the Dread Wolf quest, I am stuck.  I now have a quest marker for a location to find Mythal.  I ran around the island for a while and then gave up and hit the internet to find out what the next step is.  

My understanding is that I am to follow the long tunnel that appears to the other side of the island.  I poked around and there is a new dock that was mentioned in the internet discussion.   I also looked all through the building that was there - read the letter on the steps and interacted with the orb inside.   When I got on the boat, it took me back to the middle dock - right by my own front door (eluvian) as it were.   I attached a screenshot of where I am.   I spent a lot of time on this quest.   I lost track of one of the statues and had to re-visit every single site in the crossroads for them.    Best as I can tell, I have done every other quest but "When Plans Align" that will take me to the Cobbled Swan and is clearly labelled as taking me to the end of the story.   

I have restarted my computer and the game.  My computer is good enough that I have not had a single pause or bump while playing.   I am going to check out "When Plans Align" but it does not make sense for it to be labelled as the final direction if I have to do that before finishing the side quest.

Please let me know if there is anything I am missing.