To recommend is the journey to us by airplane to Athens and to go on by a rented car, that is cheaper to rent from your country than here in Greece. The flight time is approx. 2.5 until 3 hours starting from middle Europe, respectively in a direct flight.
The journey of the approx. 300 km route from the Athens airport to Gythio is about 3.5 to 4 hours with about half of it as a motorway and a partial expressway, and in addition a well-developed highway.
It's also possible to do the journey to Greece by car using one of the many different ferries starting in Italy. Daily ship routes are alternatively starting from Venice with approx. 37 hours as well as from Ancona with approx. 21 hours passage duration - in each case to Patras as arrival port. Also from Patras as well as from Athens it needs approx. 3,5 until 4 hours travel time over Tripoli and Sparta to Gythion.
Here is a link to websites of the leading shipping companies Superfast-, Minoan- und Anek-Lines.