"Website does not list the location any longer, and doesn't seem to exist in reality either"
The place has gone or never existed. A user of Organic Maps application has reported that the POI was visible on the map (see snapshot date below), but was not found on the ground.
OSM snapshot date: 2026-03-10T00:09:11Z
POI name: SATS Vasagatan
POI types: leisure-fitness_centre
 #organicmaps android 2026.03.12-2-FDroid