"Undying Dusk" could claim to be the longest choice adventure book ever written.

Lucas Cimon's retro RPG, available for free on Itch.io, does not immediately jump out at you. That is, until you realize that the game is effectively one giant book, each page a frame in a vast labyrinth.

The game works just like any old paperback adventure book. But instead of explicitly stating "turn to page 56 and defeat the goblins," each page has a fake UI filled with instructions, actions, and menu buttons that link to other parts of the document. There are also musical cues, a soundtrack button that opens a web browser and plays a fantasy song.

Cimon claims that, as far as he knows, this is "the first video game in PDF format." While that may not be entirely true (a quick search reveals a simple crosshairs game and a now-broken maze), Undying Dusk is certainly the most elaborate, with 10 locations, an overworld, and a cutscene-driven plot in a fully realized fantasy world. In the spirit of the old adventure games, it is also quite brutal, with thousands of game over screens and a single path to victory.

Undying Dusk is a free download; Cimon recommends playing it in Sumatra, but it should play in most PDF browsers (except Adobe Reader for technical reasons).