bornholm • castles & fortifications • Hammershus • Gamleborg • Lilleborg • Rispebjerg • Christiansø • round churches • Dueodde
Castles and fortifications on Bornholm
Bornholm’s historic castles, hillforts, trenches and fortifications tell the story of a strategically placed island in the Baltic Sea. Over the centuries, Bornholm saw battles, raids and power struggles — and traces of that past are still visible today. Visit the ruins of Hammershus, the hillforts and ramparts in Almindingen and Paradisbakkerne, the fortifications in Rønne, the fortress island of Christiansø, and the WWII bunkers at Dueodde.
Must-see
Hammershus
Best for
families • couples • history lovers
Style
roadtrip • short walks
Tip
2–4 stops per day
Why does Bornholm have so many fortifications?
From the Middle Ages to the 20th century, Bornholm’s position in the Baltic made it strategically important. That’s why, alongside the monumental ruins of Hammershus, you’ll find hillforts and defensive ramparts (Gamleborg, Lilleborg, Rispebjerg), the defensive character of Bornholm’s round churches, the town fortifications of Rønne, and WWII bunkers at Dueodde. For a full-day trip, take the boat to Christiansø — a fortress island in the Ertholmene archipelago.
Hammershus – the largest medieval castle ruins
Hammershus is Bornholm’s most impressive historic site and one of the island’s top attractions. Construction began in the 12th century, and over time it grew into a powerful fortress protected on three sides by steep rock walls. The castle was once the seat of church dignitaries and later changed hands during shifting power in the region. After 1743 it was no longer inhabited, and in 1822 it was placed under protection.
Rispebjerg – Bornholm’s oldest fortifications
Rispebjerg (east of Pedersker, by the Øle Å river) is considered Bornholm’s oldest known defensive site. In the Iron Age (around 100–300 AD) it functioned as a fortification with ramparts, a palisade, towers and a walkway, surrounded by a moat — with the river protecting one side. Today the wooden structures are long gone, but the earthworks and layout are still clearly visible.
Gamleborg (Almindingen) – a Viking-age stronghold
Gamleborg in Almindingen was the first major fortified complex on Bornholm. It was at its peak during the Viking Age (roughly 800–1100) and served as the island’s main fortress. The site measured about 264 × 110 m. Around 1100 it was further strengthened, but later abandoned in favour of Lilleborg, built about 700 metres away. Today you can still trace sections of foundation walls, earth ramparts and the former gateways.
Lilleborg (Almindingen) – the royal fortress of the 12th century
Lilleborg (“Little Castle”) replaced Gamleborg as the royal fortress on Bornholm in the 12th century. It was a centre of secular power and an alternative to Hammershus, which was linked to church authority in the north. Nearby Lake Borgesøen formed part of the defensive system — access once led across a wooden bridge. Today, the remains are mainly the foundation walls and the outline of the fortress on the hill.
Gamleborg (Paradisbakkerne) – a hillfort in a wild landscape
Paradisbakkerne is a hilly, wooded area in eastern Bornholm — with ravines, rocky outcrops, heathland and lakes. Hidden in this terrain are the remains of an old defensive site known as Gamleborg. You can still spot parts of stone walls and foundations, but the real star here is the dramatic nature around it.
Round churches – Bornholm’s sacred “fortresses”
Bornholm’s round churches combined worship with defence: narrow windows, strategic inland locations, and designs that were easier to protect during attacks. Today they have conical roofs, and the four best known are in Østerlars, Olsker, Nyker and Nylars.
Rønne fortifications (Kastellet) – a town defence landmark
In the late 18th century, plans were made to turn Rønne into a fortified town to protect the harbour and the Danish fleet. The project was never completed, but parts of the defensive system remain — including the artillery tower Kastellet. Its whitewashed look echoes Bornholm’s round churches and makes an easy stop during a city stroll.
Dueodde – WWII bunkers in the pine forest
The Dueodde complex consists of German WWII fortifications built in 1942 with the aim of controlling ship traffic in the Baltic Sea. The planned installation was never completed and never received its intended artillery, but the massive bunkers remain — a stark and powerful trace of 20th-century history on Bornholm.
Christiansø – the fortress island of Ertholmene
Christiansø lies on the Ertholmene archipelago east of Bornholm and is typically reached by boat from Bornholm. The entire island is ringed with fortifications, making it one of the most fascinating military-history sites in the region. The fortress dates back to 1684 (King Christian V’s decision to expand the natural harbour), and a key episode was the failed British attack in 1808.
FAQ: Castles and fortifications on Bornholm
Where should I start if I only have 1 day?
Start with Hammershus and the nearby viewpoints. If you want a green, relaxed add-on, choose Lilleborg or Gamleborg in Almindingen.
How much time should I plan for sightseeing?
For 3–4 stops, half a day is usually enough. If you add Almindingen and Paradisbakkerne, plan a full day. It’s best to reserve a separate day for Christiansø.
Is this a good idea for families with kids?
Yes — short stops work best, especially at “tangible” places like ruins, bunkers and the round churches. Kids often love stories about defence and life in a fortress.
Is Christiansø a full-day trip?
Usually yes. Plan a separate day for the boat trip and exploring the fortress island.
Explore Bornholm with a ready-made plan
Choose what fits your trip: guided tours, bike rental, or quick planning on the map.
