[NoboruWataya]

There a number of publicly available sources, but I have used https://srtm.csi.cgiar.org/

(Near) global coverage, 90m resolution. Easy to fetch tiles with a script.

[foobarbecue]

For the benefit of those who aren't familiar: SRTM was the space shuttle radar tomography mission. 30m resolution is now available (I remember 30m being released for the first time in the 2000s sometime I think).