I played several Infocom text-based games in high school (Zork being the most famous example) and loved the Invisiclues system: a booklet with hints to the Infocom puzzles, printed in invisible ink that you swiped with a special marker to reveal the answers. I recently discovered they’re available online for all of Infocom’s games, with obscured answers that you must click to reveal.

What made Invisiclues especially fun and clever was that the booklet wouldn’t immediately give you a direct answer. Instead, it would often start with a vague solution—for example, in Zork, the first answer to “How do I open the egg without damaging it?” is “You don’t”, hinting at another who could—with the answers increasing in specificity before finally revealing the explicit solution.

(The booklets also included fake or unhelpful clues, which I found terribly amusing. In Zork, the answer to “Is the gas of any use?” is “It’s great for blowing up dim-witted adventurers who wander into a coal mine with an open flame.” Having been one of those dim-witted adventurers, I chortled.)

This is a completely niche site for People of a Certain Age and Geekiness, and I’ve already spent an inordinate amount of time exploring it.