The Jaromarsburg was a cult site for the Slavic tribe of Rani dedicated to the god Svantovit and used from the 9th to the 12th century. It was located on the northeastern tip of the Baltic Sea island of Rügen at Cape Arkona, and was protected on two sides by the cliffed coast and from the land side by a Slavic burgwall.
At Cape Arkona in recent centuries, sections of the cliff tops have continually collapsed into the sea, which is why the remnants of the Jaromarsburg today mainly comprise the castle ramparts. Based on a loss of 10 to 20 metres per century, it is believed that the current area within the ramparts represents only a third of the original total.
Wikipedia https://en.wikipedia.org/wiki/Jaromarsburg
Address 18556, Germany
Coordinates 54°40'35.536" N 13°26'12.084" E