In that final office area there is a link to a cave much like the ones that had those pillars that you went around collecting at the beginning of the game. This one has two levels. The top level has a huge hole in the middle leading to the bottom level, which has a pool of water in the middle. That's the Bahro cave I'm talking about. It can only be reached via the lining stones at the end of Ahnonay and Er'cana.
If you look at your bookshelf in your Relto, at the top of each book there is a metal tab. On each tab is a symbol. The first several books has that hand symbol of them, and reperesent that part of the game that we refer to as Uru Prime (it was the part that was included in the original release of Uru). The next few books have a depiction of the Arch of Kerath (looks like a stretched out trapezoid) and represent the content included with the "To D'ni" expansion pack. The final books have that shell symbol on them and represent the content included in the "Path of the Shell" expansion pass. When I talk about the PotS books, those are the ones I mean.
For names, you really should be reading the DRC books that are scattered around. One is right next to where you found the linking books to Ahnonay and Er'cana back in the Watcher's Sanctuary (the Age with that big stone ball behind the door). Those journals, besides providing the names of places) also give a lot of context to those ages, provide the "story", and can sometimes offer valuable clues in order to complete those Ages.
You are done with Ahnonay, the Ahnonay Cathedral, and those things. You should be moving on to Er'cana, the other age on you shelf. Easiest way to recognize it is the Age with the elevated train tracks. If you don't have this book, go back to where you originally got the book to Ahnonay and check out what you missed.