By non-overt, books that weren't intended to be philosophical but might have unintentionally taught something meaningful.
Non-overt example:
The Golem and the Jinni by Helene Wecker
It's theme are about two different peoples in a new world trying to adapt to this strange life and feeling incredibly lonely, before meeting each other and filling that void.
Obvious choices are:
The Stranger by Albert Camus
Nausea by Jean-Paul Sartre
Candide by Voltaire
The Alchemist by Paulo Coelho
Straight philosophical discourses: (good but looking for a story)
The Republic by Plato
by Sol_Freeman