The Hindenburgdamm or Hindenburg Dam is an 11 km-long causeway joining the North Frisian island of Sylt to mainland Schleswig-Holstein, off the coast of Germany. It was opened in 1927 exclusively for rail transport. Before the causeway was built, the connection to the island was at the mercy of the tides, and in winter, the ice in the Wadden Sea formed an impenetrable barrier. The crossing took about six hours in adverse weather and flow conditions lasted longer. As the seaside resort of Westerland, on Sylt, became increasingly popular, officials started planning for the rail causeway.

The original plan was to build a train route from the port at the Hoyerschleuse to the island, but after World War I, Germany was obliged to cede the Hoyerschleuse to Denmark while Sylt remained part of Germany. Owing to the new border, the old route to Sylt was now cut off, except if travellers wanted to go to the trouble of obtaining a Danish visa to make a short trip through Danish territory. Because the situation was unacceptable, the causeway re-routed entirely through Germany.

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