This is where the ousted Greek royal family lived from 1871 to 1968. The palace is part of a large property, now confiscated by the state. The building is empty. Most objects, artifacts and precious items were taken by the former King over the years and many of them were auctioned in London some weeks ago.
The place is more than 15km out of Athens and is now part of Parnitha National Park and the whole area is open to the public. I, actually, met many tourists walking the area and many families trekking. The palace and all the other buildings are closed though.
More pictures to follow.
Read more in Wikipedia
See the area in Wikimapia