The Pindos Mountain Range is the spine of mainland Greece, dominating Upper Macedonia and inland Epiros. It's not the highest: higher than the American Blue Ridge, but notably lower than the American Rockies, never mind the European Alps. Yet the sheer nature of its geography makes it daunting. Good passes are few, and in winter, snow covers the peaks, but the valleys aren't as cold as one might expect. Ruggedness works against unification, so down to Philip's day, the cantons of Upper Macedonia were independent kingdoms with their own ruling families, and Epiros was ruled by a council of different tribes in the region, of which the Molossians (Myrtale-Olympias's family) were foremost. Philip brought in the highlands early in his reign, and by marrying Olympias, gained Epiros first as an ally, and later virtually as a dependency.
Aside from the formidable mountains, another features of the highlands is the presence of several lakes, the largest being the very deep Lake Ohrid (ancient Lykhnidos). Similarly, the headwaters of the mightly Haliakmon River are found in the southern highlands. The headwaters of the Loudios and Axios Rivers are further north (the Axios, modern Vardar, reaches up into the Republic of Northern Macedonia). The abundance of water, as well as pine-covered mountainsides, renders a different landscape from the Greek south, or even Lower Macedonia, and might explain the importance and influence of women in these areas (and Illyria), where survival demanded "all hands on deck."
UPPER MACEDONIA: Elimeia, Eordaia, Orestis
DODONA, Greek Epiros (shhhh on #2...)