Särkkä is a small island outside Kaivopuisto park, northwest of Länsi-Mustasaari. Särkkä is part of Suomenlinna, and a part of the Suomenlinna fortress is also located here. Särkkä was built to defend one of the passages to Helsinki, the Särkänsalmi narrow. The construction began in 1749, and the first part of the fortress was ready already in the 1750's.
The island is 250m wide, and is located approx. 500m outside the mainland, outside the shore of Kaivopuisto park. Särkkä is nowadays being used by the yacht club Merenkävijät ry. There's also a summer restaurant, the restaurant Särkänlinna.
A connection boat runs in summer from the Ullanlinna pier, next to the Café Ursula in Kaivopuisto park.