When looking for this location, I found that the town of Neapoli itself was too low against the mountains compared to some of the scenes of the house. However, after finding the right elevation in Street View, I could work out the general area that the crew would’ve filmed from.
It was clear that the general area was Vryses. Scanning the streets, I couldn’t see anything similar using Google Maps around the town so I decided to check the more famous landmarks – it was evident that the series was also used as a tourism vehicle so it did use quite a few famous places (Gorges, Churches and so on).
On checking photos of the Monastery of Kremasta, it looks like the archway we see every time in the series is still there.
Notice the same details in the Tripadvisor photo below. The style of archway, the telegraph pole and the door to the right are all still there.
In other episodes however, it looks as though another location was used for Katerina’s house. Looking at pictures of the Monastery, there are so many other archways and steps there that I assume they just used another area of the Monastery itself, but would require a visit in person to be sure.