From publisher blurb:
Rumors speak of a mysterious silver tower that shines like a polished mirror that has recently appeared out of thin air. Bizarre creatures believed to have emerged from the tower roam the land. The few learned sages that know of it suggest that the tower is really a dimension-hopping fortress. Possibly some adventurers could go to the tower to find out why it has come here?
DD4 Secret of the Silver Spire is classic-style fantasy RPG module for characters levels 3 to 7. It is designed specifically for the 1st edition of the original and everyone’s favorite fantasy role-playing game. This module has a minimal plot involving of high adventure, sorcery, and mystery that allows it to fit easily into any campaign world. It can easily be adapted to most fantasy role-playing games, including the advanced 2nd edition game, the original game, the BECMI (“Basic”) game, most old-school renaissance (OSR) role-playing systems, and most other similar game systems.
In this adventure, the player characters explore an outlandish citadel inhabited by strange creatures, such as the barzani ape-men, modrons of many types, and three-faced golden sentinels. The enigmatic overlords are the "silver masters" — alien beings made of pure energy. The tower is a maze of rooms stuffed with strange equipment and curious items these creatures have collected from all over the multiverse.