A typical weekend activity would be to get early into Nordmarka before the masses of people are trailing me to get some well-appreciated “Norwegian forest time” and that feeling of debriefing after a stressful week. The biggest forest, Nordmarka, is a popular place to come for activities, either being in the summer for hiking and biking or in the winter for cross-country skiing.
Nordmarka also has a number of nice little huts you normally can stop by at during the weekends for some light service. A coffee, a waffle or home-made bun of many sorts and a piece of chocolate tastes amazing and well-deserved after some physical activity. One of the best cabins to visit is for me Ullevålseter. This traditional cabin has a history going back to 1927 and is still run by the same family with the last name Ullevålseter. The cabin has a central location for many routes in the forest and is one of my favorites, as it is situated fairly close to several entry points. I usually reach it from Frogneseteren or Songsvann. It is about 5 km from each starting point and takes about 1 hour to walk each way.
And my preferred route would be to take the metro line to Frogneseteren, walk down to Ullevålseter, and then continue to Sognsvann before returning to the city. All in all, it is a great round trip, with the bonus that you will mostly be going downhill.