A One-Round Living Greyhawk Nyrond Regional Adventure
From the introduction:
Dire omens and portents point to a threat gathering in the ancient and fell fortification known as Onyxgate. Rumor speaks of an entire legion lost attempting to clear this den of evil. For the good of the Kingdom, will you risk life and perhaps soul to provide your King with information on this threat? An adventure for resourceful and hardy characters.
[For character levels] 4 - 12. It is strongly advised that parties do not “play up”.