When I visited Oslo in July 2020, I was on Stovnertårnet for the first time.
It is a footpath construction with viewing platforms that winds up between the trees in the Stovner district.
Stovnertårnet is open to visitors all year round and admission is free.
Stovnertårnet is located on the Fossumberget hill directly behind the Stovner Senter shopping center and can be reached from the shopping center via the footpaths Karl Fossums vei, Fossumberget or Olaus Fjørtofts vei. The closest underground station is Stovner, about 600 meters from Stovnertårnet. The underground line 5 takes 25 minutes from the central station.