Hmm, regarding the answers: Why not allow answering "customers only" like for playgrounds and parking? For example, there may be observation towers within an amusement park, zoo, water park etc.. These observation towers are certainly not private, but also only available to those that are customers of that park.

Hmm, there are only 60 towers currently tagged this way: https://overpass-turbo.eu/s/2eDw

We would also need to find some phrasing that makes it clear that a normal observation tower, which everyone may enter after paying, does not count. Maybe: "Who may enter?" "Customers of a larger place, such as a amusement park, or museum"?

Just use the same wording as in the playground or parking fee quest? Alternatively, add a hint along the lines of ... "Regardless of whether entry is free or paid."

Also, by the way, I find the icon a bit lazy. There is no need to make this monochrome. On the other hand, I haven't found a good (idea/template for an) icon looking in image search.

One might just use the icon in res/graphics/building/tower.svg, though.

I'll implement my suggestion.