The Horn Series by J. Kathleen Cheney

From the world of Dreaming Death: The chief of the Oathbreakers, Amal Horn is one of only a handful of people aware of the true power the abandoned underground Fortress of Salonen holds. The Cince Empire wants its secrets, though, and will do anything to get someone inside. When the Horn find a stranger trespassing on the glacier below it, they realize the Cince have formulated a new plan of attack... moreFrom the world of Dreaming Death: The chief of the Oathbreakers, Amal Horn is one of only a handful of people aware of the true power the abandoned underground Fortress of Salonen holds. The Cince Empire wants its secrets, though, and will do anything to get someone inside. When the Horn find a stranger trespassing on the glacier below it, they realize the Cince have formulated a new plan of attack. Now the Horn Family must decide whether to wake the sleeping Fortress so it can defend itself against the Cince…or kill it forever. less

Amal, Lady Horn, has always been called rash. She makes decisions far too quickly for the elders of the Horn Family. Bringing home a mysterious foreigner-one who has ties to her people's ancient enemies, the Cince-is bad enough, but now she's taken him as her lover. She might even want more from him.Dalyan is an Original, a copy of a man long dead... moreAmal, Lady Horn, has always been called rash. She makes decisions far too quickly for the elders of the Horn Family. Bringing home a mysterious foreigner-one who has ties to her people's ancient enemies, the Cince-is bad enough, but now she's taken him as her lover. She might even want more from him.Dalyan is an Original, a copy of a man long dead. The elders of the Horn Family thought they could use his singular knowledge to resurrect an ancient Fortress, a sentient underground city long abandoned by its people. But when Dalyan can't access the memoires of the man from whom he's copied, the elders begin to ask whether he's an unfortunate liability instead. For Amal's sake, Dalyan is determined to prove them wrong. Together Amal and Dalyan work to build a coalition to raise the hidden Fortress, but they'll need the help of Amal's friends, of the Oathbreakers spread across the country, and-if possible-the king himself. less