Grefsen is a neighbourhood of the city of Oslo, Norway. Grefsen was a part of the municipality of Aker before the Second World War, later incorporated into Oslo. Together with Kjelsås, Grefsen then formed the borough Grefsen-Kjelsås until 1 January 2004, when they became part of the new borough of Nordre Aker. The railway line Gjøvikbanen goes ...