This Baltic Sea island has 570-million-year-old volcanic rocks, a medieval church with defensive walls, and calm swimming coves. Population doubles to 16,000 in summer.
On Alnön, an island in the Gulf of Bothnia near Sundsvall, you can walk among 570-million-year-old volcanic rocks, swim in the protected Släda cove, or visit a medieval stone church with thick defensive walls. The island's population grows from 8,000 to 16,000 in summer when seasonal residents return to their waterfront houses.
Getting to Alnön
The 1,042-meter Alnöbron bridge connects the island to mainland Sundsvall. You can drive across this bridge, which opened in 1964, to reach any part of the 15-kilometer-long island. Local buses run regular routes across the bridge, making the island accessible for day trips from Sundsvall.
Volcanic Formation
A volcanic eruption 570 million years ago created Alnön's rocky landscape. The northeastern part contains carbonate mineral deposits, forming one of the few carbonatite volcanic complexes worldwide. Geologists come to study alnoite, a distinctive rock containing biotite and melilite minerals, which was first discovered and named after the island.
Summer Activities
You'll find several swimming spots along the coast. Släda beach has shallow, calm waters where children can wade safely, while Röde cove drops off to deeper waters suitable for swimming laps. In Vi and Hovid, small restaurants serve fish caught in local waters during summer months. Former boathouses now function as cafes, selling coffee and kanelbullar (cinnamon buns).
Historical Sites
The Alnö Old Church, built in the 12th century, has thick stone walls that once protected villagers during conflicts. Today, you can attend summer services, weddings, and baptisms in this medieval building. The island's industrial period began in the 1860s, when steam-powered sawmills transformed Alnön. Between 1860 and 1897, eighteen sawmills operated here, and the population grew from 950 to 7,000 residents.
