After killing the boss early, I briefly stopped at Adal Matar to pick up Captain Ghoragdag (good work on guarding the two orcs btw lol), and informed Braga Clearwater of her brother's valiant death, inviting her to move anywhere else instead of living on a lonely frozen mountain. She refused. Respecting her choice, Ghoragdag and I headed right back up to Death Mountain to find ways into the many other chambers I didn't have access to yet.
This time I found a fence that I could whirlwind sprint over (with Ghoragdag being more practical just climbing over I guess), and found another key in a shrine that gave us access to "The step of giants" - an odd tunnel that housed giant spiders and three of the big guys who normally have mammoths. Sniped the lot of them and found a key... to the tower I broke into earlier? Lol.
We mangle giants.
Fortunately it also opened up a catacomb / prison area filled with draugr who for some reason had three hostages, a khajit, a nameless tortured lady and a chick named Nerelia who was the only one who wanted to get out of there so we took her along and soon discovered that she too was dragonborn!? She uses shouts. Well so do draugr, when you think about it but anyway...