Mustavuori Forest and the Östersundom bird waters form a protected Natura 2000 area on the eastern edge of Helsinki. The draw is quiet nature rather than spectacle: varied forest, wetlands, and good birdlife within reach of the city.
It is a strong choice for travellers who want a wilder Helsinki walk than the central parks can offer. Bring binoculars if birds are your thing, and expect paths rather than polished tourist infrastructure.