The Serpent by Jane Gaskell

The journey to Atlan begins with Cija's being freed from the tower in which she spent her childhood. Raised thinking that males no longer existed, and that women had evolved beyond them and hatched from eggs, Cija is rudely thrust into the real world with the task of seducing and killing the first man she has ever seen. This is great fantasy about a rousing adventure, lust, love, suffering, and cruelty and an unusual woman.