Sprogø is a small, protected Danish island, which is located in the Great Belt, the strait that separates the main islands of Funen and Zealand. It lies about halfway across the strait, 6.7 km from the Zealand shore and 8 km from the Funen shore.
Today, the island forms part of the Great Belt fixed link, and is connected to Funen by a road and rail bridge, and to Zealand by both a road suspension bridge and twin rail tunnels. The island is crossed when using the link. During the construction, the island was drastically remodelled, with land reclamation increasing its area from 38 to 154 hectares.
There are remains of buildings on the original part of Sprogø from the beginning of the 12th century, a fortress built under king Valdemar the Great. During construction work, extensive archaeological investigations were undertaken, and among other findings it was revealed that the first inhabitants arrived more than 8,000 years ago.
The island has no permanent population today, but is used by Sund og Bælt, the company that owns and operates the bridges. It is also a nature reserve, and tours of the island are organised.
A darker part of the island's history are the years between 1923 and 1959, when the island was used for containment of women deemed pathologically promiscuous, the main concern being unwanted pregnancies. At the time it was considered a very humane approach, given the fact that they had previously been confined.
Sprogø was a station for the semaphore line across the Belt, Storebæltstelegrafen, between Nyborg and Korsør, in operation between 1801 and 1865.
The lighthouse, which can be seen in the picture, was built by the mail service in 1868, replacing an older structure from 1809. It was built on the foundations of the 12th century fortress.