Ertholmene

Ertholmene is a small Danish archipelago in the Baltic Sea, northeast of the island of Bornholm, composed chiefly of the inhabited islands Christiansø and Frederiksø with several smaller skerries.

The islands preserve extensive 17th‑century masonry fortifications, narrow granite streets and timber houses clustered around a central harbour; they are managed as a protected area with notable seabird colonies and marine life.

Fortification works and the settlement were established in the late 17th century as a naval and coastal defence point, and the islands later developed a permanent civilian community while retaining their military structures.

Ertholmene lies off the northeast coast of Bornholm and is reached by passenger ferry from Bornholm’s ports (commonly Gudhjem); the islands are small, largely pedestrian and exposed to open Baltic sea conditions.

• Ferry access: Regular passenger ferries operate from Bornholm (typically from Gudhjem) during the tourist season; check timetables in advance as services are limited.
• Practical note: The archipelago is protected and has a small year‑round population; most visitors explore on foot and there are no cars on the main islands.

What to See #

• Christiansø: Christiansø is the largest inhabited island and contains the harbour, ramparts and the majority of the preserved 17th‑century fortress structures.
• Frederiksø: Frederiksø is linked to Christiansø by a small bridge and contains residential buildings and some of the smaller harbour facilities.
• Outer skerries: A scatter of smaller skerries and rocks surrounds the two main islands and form part of the protected Ertholmene archipelago, important for seabirds and seal haul‑outs.