Sentrum (City Center) in April

May through September gives you the best of Oslo's compact summers. July brings 18-hour daylight and outdoor concerts in Frogner Park, but also cruise ship crowds and hotel prices that spike 40%. June offers the sweet spot - long days, fewer tourists, and the city's outdoor cafés finally opening their terraces. September surprises visitors with mild weather and autumn colors along the Akerselva river. Winter transforms Sentrum into a Nordic wonderland, but daylight shrinks to 6 hours by December. The Christmas markets around Spikersuppa start in late November, and ice skating appears in front of the National Theatre.