Mærradalen is a narrow valley in western Oslo, roughly two kilometres long, stretching between Ullernchausséen and Sørkedalsveien. At the bottom flows the stream Mærradalsbekken, which gives the valley a humid microclimate — creating ideal conditions for lush, moisture-loving vegetation. The valley features old forest, rich undergrowth and a varied flora including rare plants, and is home to a number of bird species such as owls and forest-birds. There is a marked footpath through the valley, making it a valued recreational green space within the city.