The Sand Castle is a small hotel exclusively for children located within the Costa Navarino Resort in Messinia, Greece. It hosts recreational and educational activities designed for children ages 5-7 and 8-12 years. 

One of the most impressive architectural aspects of the castle is the children’s private areas, which are designed according to their own anthropometric scale and are part of an open "neighborhood." The kids get community, privacy, and creativity at the same time. No parents allowed!

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[via MyDesignStories]