Oslo Gressholmen is included in my addon scenery for MSFS
with nine old water airports, in use ca 1923-1936.
See main scenery page, under Sweden:
For History see webpage:
"Water Airports in the Nordics, Scandinavia, 100 Years Ago"
The zip-file: Oslo-Gressholmen-dummy.zip
is only added to get this link page under "Norway" in flightsim.to, and map coordinate.
Bo Justusson, Stockholm