Kastania with its Byzantine church was worth our visit, but we found out the hard way that there is another Kastania nearby, on the east side of the Mani. Coming from further south on the peninsula (Dirou Caves), Google Maps chose the wrong Kastania. We did not want to retrace our route from Kardamyli so we crossed the peninsula and headed north trusting Google. We reached the wrong Kastania and found nothing there, just a small half-deserted hamlet. So we let Google maps suggest a route back to Kardamyli and it sent us up a narrow hairpin road to a pass, where a modern monastery (Moni Panagia Giatrissa) is located. This was worth a visit in itself but we had no time by then after our drive. By now it was approaching sunset and we had executed an all-day, tortuous "U-shaped" drive and were not that far from Kardamyli, according to Google.
We had seen no vehicles for an hour but found a forlorn traveler from France standing by the monastery who had also visited the wrong Kastania -- on foot. We gave her a ride. Google Maps (ours and hers) said to continue, but what confronted us was a steep dirt road, hardly more than a track, down the west side of the peninsula from the monastery. We plunged down it in our Peugeot but the road deteriorated and we were soon bottoming out frequently with no way to turn around. There was no question of turning back because our 2WD car did not have the traction to back miles up the steep grade, we really needed an SUV. One extra-deep rut or a boulder in the road would have stopped us in our sedan for the night, unable to continue. Fortunately our French trekker knew the area and began to recognize the terrain below so she encouraged us to continue, and we ultimately emerged onto a one-lane paved road and soon found the real Kastania.
Though unplanned travel often makes the best memories, this could have turned into a bad experience for us and I wanted to warn others about it. Make sure your Google Maps chooses the correct Kastania!