Far, Far from Holland...
Relax, while there is a good probability that you have at least a small contact-high from all of the marijuana floating through the San Francisco atmosphere, chances are you’re not hallucinating. It’s a well publicized fact here in San Francisco that you can not get a contact-high from mushroom tea, so more-than-likely, you are not inadvertently tripping.
And yes, that is a giant windmill at the far western end of Golden Gate Park.
No, it doesn’t work.
As I intend to provide factual information here at SFIW.com, I have conducted some extensive research about the wayward windmill (i.e. typed “San Francisco Windmill” into google) and have uncovered an incredible conspiracy! It seems that an organization called Golden Gate Park Windmills (plural!) insists that there are TWO windmills at the far western end of Golden Gate Park. Even though this Street View from google maps clearly shows only one!
Perhaps I am hallucinating? San Francisco is Weird, but at least there’s a windmill. Or two.
San Francisco is Weird 
There are two, just one is missing all the sails off the top, so it just looks like a small decrepit tower