The Shuttle Radar Topography Mission (SRTM) was a NASA mission to provide digital elevation data for the entire world. The data is free and available for use by anyone. A good place to find data is on this website.
This library provides simple functions to read and convert SRTM data. Both the SRTM1 and SRTM3 data are supported.
image.go provides simply functions to convert the SRTM data files to Go's image implementation, which can be processed further.
The cmd subdirectory contains simple scripts to convert the SRTM data to gray scale images directly.
The docs subdirectory contains NASA's SRTM documentation, which can currently be found on the Web Archive as the webpage does not exist anymore.