Visit the world's earliest naval base and fortress which was established in 1684. Take a daytrip to the fortress islands Christiansø and Frederiksø - Denmark's easternmost point.

Popular destination to the north-east of Bornholm
The Ertholmene Archipelago lies temptingly on the horizon north-east of Bornholm. The archipelago comprises the inhabited islands of Christiansø and Frederiksø, Græsholmen (a bird sanctuary) and a number of islets and skerries. Over the centuries the islands have been transformed from a collection of remote, rocky knolls jutting up from the sea into a popular tourist destination.

Sense the presence of history
This all started in 1684 when Denmark’s king Christian V (1670–1699) decided that a fortress should be built for the ships of the Danish navy in the Baltic Sea. Under the Treaty of Roskilde in 1658, Denmark was stripped of the now Swedish provinces of Scania, Halland and Blekinge, making it more vital than ever to monitor the movements of the Swedish navy in the Baltic Sea. A natural harbour located between two of the islands in the Ertholmene Archipelago is where the fortress of Christiansø was built, making it the first naval base in the world. The first structures to be built were the two distinctive cannon turrets St. Tårn (Big Tower) on the island of Christiansø and Lilletårn (Little Tower) on the island of Frederiksø.

Impressiv edifice
Bastions and ring walls facing the open sea were built on both islands. The many other buildings of the fortress were well protected behind the fortifications. It was an impressive edifice that was enlarged and rebuilt throughout the era the islands served as a fortress. Danish naval ships could seek protection in the harbour, stock up on drinking water, and repair damage sustained during their expeditions in the Baltic Sea. Christiansø was abandoned as a fortress in 1855 as this type of fortification had become outdated. It is still intact, however, as a tangible depiction of a segment of Denmark’s cultural history.

The community today
Today, this historic setting is inhabited by a small civilian community of around 100 people. The islands of Christiansø and Frederiksø have a school, church, lighthouse, post office, library, community centre, a museum, a tenting area, a grocery shop and an inn. The islands have their own fire-fighting and rescue services, power station and water works.


You can preorder your tickets for the ferry to Christiansø from the harbour in Gudhjem on our website.

From DKK 230,- for adults / DKK 125 for children (6-14 yrs)



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Contact information

Tlf. +45 5648 5176




Ejnar Mikkelsensvej 25

3760 Gudhjem

Telephone hours

Monday – Friday 10 am – 3 pm

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