The Diamond-Square Algorithm is the natural first stop for generating artificial landscapes.
The algorithm itself is beautifully simple (more details below, and on its
Wikipedia page).
But a casual implementation ended up not working at all, prompting me
to look for an existing implementation to learn from. However, most
implementations I found looked hideously complicated (or just hideous),
not necessarily correct, and/or used out-of-date programming languages
and styles. It therefore seemed like a good idea to create a clean,
simple “reference” implementation of this algorithm, using a contemporary
and widely known programming language and style.