thumb|North Frisian coastline before 1362
thumb|The island of [[Strand (island)|Strand after the Grote Mandrenke (Danish: Den Store Manddrukning) with German and Danish place names]]
thumb|Rungholt and Strand in the Middle Ages, on a map from 1850
Rungholt was a low-lying settlement in North Frisia, in what was then the Danish Duchy of Schleswig. The area today lies in Germany. Rungholt was flooded, with massive erosion, when a storm tide (known as Grote Mandrenke or Den Store Manddrukning) hit the coast on 15 or 16 January 1362.
Location
Rungholt was situated on the island of Strand, which was largely destroyed by the Burchardi Flood of 1634; remaining fragments include the Nordstrand peninsula and the islets of Hallig Südfall, Pellworm and Nordstrandischmoor, while the rest now forms tidal flats in the surrounding Wadden Sea.
In 1921, ruins believed to represent Rungholt were discovered around Hallig Südfall: wells, trenches and part of a tidal lock. In June 2023, the German Research Foundation announced that researchers had confirmed this identification, and had already mapped 10 square kilometers of the area including key features such as a church. Detailed archeological investigations of the remains of buildings, dykes and a harbour have been published. Possibly 30 settlements were destroyed, and the coastline shifted east, leaving formerly inhabited land in the tidal Wadden Sea.
The Sinbadventurers (German: Die Hamburger Sindbadauken) is an opera for children composed by with a libretto by Francis Hüsers. It was commissioned by the Hamburg State Opera and was first performed on February 8, 2015. In the opera, three children set out to discover the lost gold of Rungholt. In the Interlude before the final act, the main character, Lotte, tries desperately to warn the citizens of Rungholt of their impending destruction by reciting verses from Liliencron's ballad.
German singer Achim Reichel put Liliencron's poem to music on his 1977 album '.
German band Santiano released a song called "Rungholt" in their 2015 CD "Von Liebe, Tod und Freiheit". It also includes verses from von Liliencron's poem.
Theodor Storm mentions Rungholt in his novella Eine Halligfahrt.
Local myth has it that one can still hear the church bells of Rungholt ringing underwater when sailing through the area on a calm night.