Olivier Bordellès, Arithmetic Tales, Springer.
It's not entirely focused on algebraic number theory which is the subject of the last part of the book, but almost no prerequisite is needed. The author introduces all necessary elements about Galois theory and whatever might be needed to start studying algebraic number theory. This book is a revised and augmented English version of his former book "Thèmes d'arithmétique" which is already a very nice work focused on elementary and analytic number theory, with many exercises, and that suits people from "bac +1 level" to master's degree (I don't know the American educational system, so I stick with the French one, sorry).