Spire's Reach is an adventure hook based around an enigmatic structure of the same name. This structure is a black box, a puzzle for players to discover and try to solve. The building can be used as an important element in an adventure, but one which players will need to attempt to solve in order to gain entry.
This is aimed at d100 systems but is generic enough in nature to be adapted to others.
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One page is cover and one the front matter.