The Peloponnese is jammed packed with great beaches and some very important ancient and medieval sites and its only a couple of hours from Athens by car!A good trick to see the Peloponnese and the Aegean islands without returning to Athens is: depart Gythion, Peloponnese by ferry for Crete and from Crete to many Aegean islands. Crete has 3 major ports with differing connections and schedules, with Heraklion being the capital and largest port; with most connections and airport.
There are 7 Prefectures (nomes) in the Peloponnese. The nome names in use today are the ancient ones with spelling variations. (Elia vs Ilia) During the middle ages, under the Venetian and Byzantine Empires the Peloponnese was affectionately known as the The Morea. Possibly for its mulberry leaf shape.
The Peloponnese is a great place to drive in but not in August and only if you exercise caution on the winding seashore roads of the hinterland.
Due to the modern super highway from Athens to Tripoli drivers can reach the very heart of the Isle of Pelops in a couple of hours, smack dab in the middle of nowhere.
After that the mountain and many coastal roads revert to the winding, climbing, switchbacking, hairpin paths they were surely formed from.
To be fair there are some perfectly fine roads on the flatter parts but many others pass through mountain passes or the winding shore on mountains or both.
The rental cars in Greece generally have stick shifts unless you ask for automatic which are like corocodile tears.
When going down hills be sure and downshift. You knew that, but do it anyway to save the breaks.
The topography is magnificent in many places but no Sunday drive at the best of times if you really want to go to several places.
If its high season when you visit (late July or August) then you'll get stuck on one lane roads behind other vehicles and heavily ladden dali-kas or semi trucks more often than you'd like.
It is not the best time to plan a drive around the Peloponnese.