Looking at European capitals from an urbanistic point of view, they all strive to bring, more or less successfully, nature inside the city. Or describing it abstractly: we have an urban environment with spots of green in it. With Oslo, I feel it is quite the opposite – what we have is nature with patches of city in it. In fact, we are living inside a big forest dotted with lakes, some very pristine and untouched, others easily accessible and with more of an urban touch.
Nøklevannet lake is one of my favourites and is located on the east side of the city. One can reach it from Haraløkka parking or a short walk from Bøler subway station. It has a neat little bathing area called Bråten badeplass, with a small sandy beach for children and wheelchair access. The water in summer usually gets super warm and is a perfect option for those who find jumping into the Norwegian sea too extreme.
A zillion forest trails criss-cross the area that are interesting to explore on foot, by bike or on skis (the latter I would only recommend in combination with snow). In summer, you can expect to stumble upon big areas of blueberry bushes; in winter you might be welcomed by the northern lights.
I strongly urge you to take a break from downtown and go have a small taste of Norwegian nature – all its shades and seasons are equally impressive.