Interesting, I've planned similar shots before and used different tools that serve a similar purpose. The Photographer’s Ephemeris has neat visualizations: https://photoephemeris.com/

NASA's Horizons ephemeris is also pretty good at preparing data for this purpose. I've used it with a little script to check when the sun/moon will be in a given box. This hengefinder looks neat and really streamline for its purpose though.

It would be nice to be able to access the website on a smartphone (even if the experience is suboptimal), instead of denying access.

Smartphones have the huge advantage of direction sensors (3D magnetometer and gyro). I remember using apps like Google sky map (or something like that) way back in 2011 to look at satellites and planets.

Manhattanhenge is cool but people standing in the middle of street for it is pretty nuts.

it’s nuts that more streets in manhattan aren’t pedestrianized

Stonehenge of course, famously not a henge.

Mobile app not available in your country. :(

then use a stick™

hint, watch the sticks shadow

other hint, can use almost anything that casts a shadow, as a stick substitute.

* even more hints availible with stick™ pro

I’d like to subscribe to stick™ pro! I tried a piece of string and it waved around in the wind and didn’t work, so I think I may need a paid service for this.

It would be good to also have the option for alignment with sunrises in addition to sunsets.

For instance in Houston the sunrise aligns with Texas Avenue around the June solstice.

Consequently, there are no sunset alignments for the downtown skyscrapers.