Secret of the starry depths is a very short game about a wannabe cave explorer who discovers that when things seem too easy, there's usually a reason. It was originally a demo for the experimental authoring system Adventure Prompt, but when the latter proved to be a dead end, the game was adapted for the Z-Machine and parser-based gameplay. You can still try the original above if you prefer, but it's rather more sketchy and less convenient to study or modify.
The game was first created in the autumn of 2016, updated in the spring of 2018, and ported to Inform in May 2020.