Prora is officially the longest building in the world, its length after construction was 4500 meters! By the way, the second place among residential buildings is a house in Lutsk (Ukraine), 1,750 meters long (google.maps). If we take into account any man-made structures, then only different defensive walls, like the Great Wall of China, are longer than the Prora.
In 1939, construction was stopped due to the outbreak of war, however the building itself was built. The rooms were small, 5 by 2.5 meters, with two beds, a wardrobe and a sink. Toilet and shower were shared on the floor. After the war, refugees from East Prussia (now the Kaliningrad region, Russia) lived here. From 1948 to 1953 the building served as a barracks for Soviet soldiers. During training, Soviet sappers blew up a significant part of the building, which was subsequently demolished. Therefore, now the building is not so long.
That's how it looked after the end of construction.
Since 2004, the buildings have been sold to investors. It will house apartments, hostels, hotels and homes for the elderly. Construction of the resort is planned to be completed in 2022.
As of 2019, the ruins of Prora can be seen only here N 54 27.467 E 13 34.033.
The most preserved and not yet restored part can be found here N 54 26.368 E 13 34.518, there is also a museum Dokumentationszentrum Prora (http://www.proradok.de/en/).
Getting there: by train to Prora station or by bus to Prora Nord bus stop, use bahn.de.