I am quoting the visit Oslo site, because I’ve been typing too much…

Akerselva: River walk by torchlight
Annual event in honour of the autumnal equinox in Oslo – when night and day are the same length.

A total of 3,500 torches light up the Akerselva river from north to south, creating a mystical atmosphere around the 8 km long cultural journey.
Experience light sculptures, choirs, folk music, jazz, dance, art installations, trolls and gnomes.

This was one of the installations, I can’t wait to play one of these at one point in my life!