From publisher blurb:
This module was written for play at GenCon 2009, as an introduction to old style free-form adventure gaming. It uses the Swords & Wizardry Core Rules. Swords & Wizardry is a "retro-clone" game, mirroring the rules of the original 1974 fantasy roleplaying game written by Gary Gygax and Dave Arneson. This original edition, which consisted of three booklets and four supplements, is often referred to as "0e." There are actually two versions of Swords & Wizardry: the WhiteBox version uses only material from the first three booklets, and the Core Rules (used here) make use of some, but by no means all, of the material from the four supplements.
Background
For centuries, out in the wilderness beyond civilization's reach, there has stood an enigmatic tower known as the Spire of Iron and Crystal. It is a bizarre and ancient structure; four massive, eggshaped crystals are mounted into a twisting, ornate structure of rounded metal girders, one crystal at the top and the other three mounted lower down. Moving lights seen inside the huge crystals suggest that they are hollow and even inhabited, but no one has ever discovered the secret of how to enter them. This is not surprising, for the tower is located on a broad stone ledge halfway up a sheer cliff face, the glassy walls of which have killed several adventurers who attempted to climb down to the tower almost a hundred feet below.
Over the course of the last few months, with considerable effort and some highly questionable methods, the adventurers have assembled quite a bit of information about the Spire - things not widely known, even among the wisest sages of the lands. Most importantly, they believe they know how to enter the structure safely. Once per year, the sun shines through an ancient runestone at the edge of the great cliff upon which the Spire stands; for a period of three days when the stars are aligned with the runestone, an invisible causeway manifests, connecting the highest crystal of the tower with the edge of the cliff, far above. According to the party's information, it is only during the first hour of evening, while the sun is visible through the runestone that the ramp remains in being.
This information promises to allow the party access to the riches of the tower, which are lavishly described in rumor and lore. They have equipped a small expedition and made their way through the trails of the wild borderlands to their goal: the tower and its still-unplundered riches.