In terms of coziness, Oslo is one of the best cities in the world. Rather than being the only special reason, it's a comfort generated by various conditions.
What are the conditions?
A rich landscape created by the sea and mountains. Even if old architectures remains, various kind of buildings are appropriately mixed, and there is no strictness of a city where townscape controls are too strong. By limiting the expansion of the city to increase the density of people living in the central district, suppressing cars by underground bypass tunnels that eliminate passing traffic and fulfillment of public transport resulted, a lot of people appear in the city. Besides, people doesn't interfere to others but are tolerant to various races and classes. That is very Norwegian style.
It's not comfort based on the visual effects. So, it's difficult to feel that just by circulating only tourist attractions. But, as you move around the city, you will be filled with free atmosphere.
A happy encounter of landscape, urban policies and national character is Oslo.