Strongholds of Sorcery: The Glain Campaign

From the title page: A Basic Fantasy Role-Playing Game Adventure Series For 4 to 8 Player Characters, Levels 4 to 8 Publisher's Blurb: This adventure series from the World of Glain includes four adventures featuring the fortresses of some of the most powerful wizards in the world: Castle D'Angelo, a fortress full of mad wizards; Tower of Light, a ruined fortress-laboratory in the Great Desert; House of Coldarius, an adventure featuring the home of a very old, very dangerous wizard; and Thaumerion's Tower, once home to a powerful wizard who long ago disappeared.