Lake Mälaren is Sweden's third largest lake, stretching from Västerås eastward through Stockholm all the way to the Baltic. In Västerås, the lake defines the southern edge of the city, and the harbour area has been significantly redeveloped into a pleasant waterfront district with restaurants, a marina, and swimming areas in summer.
The swimming beaches near the harbour are genuinely good — clean water, sandy areas, and usually less crowded than the Stockholm equivalents. In summer you can rent kayaks and canoes from the harbour, or take boat trips out to the small islands scattered across this part of the lake. The evening light on the water in summer, when the sun sets well after ten, is one of the city's understated pleasures.