Trollskogen, Nature reserve in Borgholm Municipality, Sweden.

Trollskogen is a 100-hectare nature reserve on a promontory at Öland's northeast tip, part of Böda Kronopark. Its eastern Baltic shore has wind-deformed, lichen-covered pines above a shingle beach; inland, pines up to 200 years old stand with about 30 broad-crowned oaks and much juniper. Cattle still graze, keeping the forest open.

Trollskogen was long protected as a Domänreservat before becoming a nature reserve within Böda Kronopark. Grankullavik, once Örboviken, served as a naval base in the 15th century, and traces of two fortifications remain. A roughly 230-metre stone wall to the south dates from the reign of King John III (1568–1592). The schooner Swiks wrecked on the eastern shore on 21 December 1926; its seven-man crew reached land safely.

The name means "troll's forest" or "enchanted forest". The Trolleken, probably Öland's oldest oak at an estimated 800–900 years, is a protected natural monument. The nature centre opened in 1973 when the Öland Bridge was built; its huts are reused forest workers' cabins from the 1950s–60s, hauled by horse-drawn sleds in winter, some still showing stove marks.

Well-marked trails with varying difficulty levels guide visitors through the reserve, with information boards in multiple languages describing local plants and wildlife. Sturdy footwear is recommended, and visitors should be prepared for uneven ground and potentially wet conditions.

The eastern shore holds the wreck of the Åland schooner Swiks, which ran aground on 21 December 1926; its seven-man crew reached land safely by lifeboat and were housed in Grankullavik. Nearby stands Trolleken, likely Öland's oldest oak, estimated at 800 to 900 years and protected as a natural monument.