The Disappeared City Center of Kostrzyn in Kostrzyn nad Odrą, Poland

The modern Polish city of Kostrzyn nad Odrą lies directly on the Oder river, which has formed the border between Poland and Germany since World War II. Prior to 1945, the city was mostly inhabited by ethnic Germans and called "Küstrin" (also listed in some places as "Cüstrin"), but the German residents were forced to leave as a result of the border changes after the war. Ethnic Poles settled in their place, although not in the strictest geographical sense: the historical city centre of Kostrzyn/Küstrin was so throughly destroyed in the war that it had become uninhabitable, so the incoming Poles built what amounted to a new city center about 1 km (0.6 miles) to the northeast.

The historical city center, once a densely-populated, fortified settlement on the Oder River, was left to fall into ruin, and was eventually torn down entirely. Today, the historical center is a free public park that has been largely reclaimed by nature. The foundations and cellars of the pre-war buildings are still visible, the main sights (like the church, city hall, and market square) are all labeled, and the original streets are still signposted, as if directing tourists around a ghostly city that still exists among the ruins.

There is a small, free museum near the former city center's entrance (next to the old border crossing) as well as a larger paid, seasonal museum in the "Filip Bastion", one of the surviving fortifications on the eastern edge of the former city center. There are few restrictions in the park and it's possible to explore the city ruins to your heart's content.