Oset and Rynningeviken is a nature reserve where the River Svartån flows into Lake Hjälmaren, about twenty minutes' walk east of the city centre. It is one of Sweden's best birding sites within a major urban area, with a network of hides, boardwalks, and viewing platforms across extensive wetlands and shallow bays.
The reserve attracts a remarkable variety of waterfowl and wading birds, with particularly strong numbers during spring and autumn migration. Over 230 bird species have been recorded here. The hides are free and open year-round, and the trails are generally flat and accessible. This is a genuinely worthwhile detour even for non-birders — the landscape of open water, reedbeds, and willow scrub is attractive, and the city feels very far away.