I'll add more. Pääsküla mägi is covered waste landfill that is reused for generating gas and using the gas in crematorium. It can not be simple natural=grassland.
According to wiki, it should be landuse=landfill +disused=yes meaning its still currently a landfill but its not used as a landfill to will more waste into it. It has multiple purposes now  but it is still a landfill and in no way a natural feature.

https://wiki.openstreetmap.org/wiki/Tag:landuse%3Dlandfill