LGBTQI+ scene
Wikipedia describes Sweden as "one of the most tolerant and accepting countries in the world towards LGBTQI+ people", and Stockholm concentrates that openness in a spread-out scene with no single cluster like Chueca or the Castro. The queer/bohemian core is Södermalm, the island south of the centre, with classic bars such as Side Track and the summer terrace Mälarpaviljongen by the lake.
The offer is compact but dense (Stockholm has ~1M inhabitants in the municipality and 2.5M in the metropolitan area, according to Wikipedia): a mix of classic bars, weekend clubs and roaming events. High LGBT visibility across the whole centre, with no need to cluster on a single street.