Carolinensiel harbour, Harbor museum in Wittmund, Germany.

Carolinensiel harbour is a museum port on the North Sea coast in the Wittmund district of Lower Saxony, where a collection of historic wooden vessels are permanently moored along the quayside. The ships sit close together along the water, and many are open to board, giving direct access to their decks, holds, and living quarters.

In the 18th and 19th centuries Carolinensiel had the second-largest tidal and trading harbour on the East Frisian North Sea coast. Its economic importance declined in the early 20th century, and when the Harlesiel harbour was built in 1953–1956 the partly silted harbour was filled in. The Sielhafenmuseum opened in the early 1980s, rebuilding began in 1986 at a cost of 1.8 million D-Mark, and the museum harbour opened on 9 September 1987.

The harbour is a protected group monument, and many buildings along its east and west sides are listed individually; three of the old buildings now hold the exhibitions of the Deutsches Sielhafenmuseum. Each year on the second weekend of August the Sielhafenfest brings traditional ships together in the harbour.

The harbor sits in the heart of the small village of Carolinensiel and is easy to reach on foot once you arrive in the area. Many of the ship decks are uneven and the passages below deck are low, so sturdy footwear and a little agility are worth keeping in mind before boarding.

The harbour is protected as a group monument, and many buildings along its east and west sides are individually listed. Three of these old buildings now hold the exhibitions of the German Sielhafenmuseum, opened in the early 1980s, which set the harbour's reconstruction in motion.