I rewatched this movie last night on the Crunchyroll channel, but it’s also on Youtube for free in its entirety (see above), in decent quality.
It’s worth watching, even if anime isn’t your thing, because it has the sense of a semi-sci-fi movie from a Western producer…but animated. It helps to think of it as a Studio Ghibli film but more geared towards adult sensibilities and pacing. Many typical anime plot elements are here: American imperialism, the “large explosion” typology/legend, science-and-mysticism*, and schoolkids doing odd things in their spare time.
And even if that doesn’t appeal to you, there’s some excellent background scene art.
* If you think of the tower much like Clarke’s/Kubrick’s monolith from the 2001 universe, you’ll be on the right track.