Teaching medieval philosophy is one way to expand one's philosophical horizons! I studied topics in medieval philosophy for some teaching in grad school. I got very interested in natural theology, divine foreknowlege and free will, and theories of the soul in the medieval period during that time. Then I began teaching it at Cal Poly the first year I got hired. The current structure of the course studies topics from the following philosophers:
Introduction to Plato, Aristotle
Neo-Platonism (Plotinus, Porphyry)
St. Augustine
Boethius - divine foreknowldge problem
John Scotus Eriugena
St. Anselm
Abelard
Avicenna
Al-Ghazali
Averroes
Maimonides
Ockham vs. Duns Scotus
Key topics besides those mentioned above: realism/nominalism about universals, negative vs. positive theology, eternality/temporality of world, bodily resurrection, Christian doctrine of the Trinity, univocity/equivocity of being, etc.