Troms Capital Tromsø Tromsø is the largest city in northern Norway and the seat of Troms, on an island 350 km above the Polar Circle. It has the Catedral do Ártico, the Fjellheisen cable car, Polaria and the Museu Polar, and is one of the most used bases for trying to see the northern lights from September to March and the midnight sun from May to July.