The Gates of Firestorm Peak (1996)

From the back cover:

Once a generation, they say, a strange comet appears in the sky overhead and the gates of Firestorm Peak swing open. Twenty-seven years ago, your father led his band of adventurers into the mysterious mountain, never to return. Now the Dragon's Tear once more flickers in the sky, and the glass gates on the mountainside beckon. Will you pass through to discover the secrets that await beyond the portal none has ever dared and returned?

The Gates of Firestorm Peak is the first adventure designed especially for use with the new rules presented in the three Player's Option books: Combat & Tactics, Skills & Powers, and Spells & Magic. While it can also be played using just the AD&D game core rules (the Player's Handbook and the Dungeon Master Guide), this adventure offers a perfect opportunity to experience all the potential of the new optional rules. One of the highlights of this package is the first Player's Option player character record sheet.

To meet the challenge of Firestorm Peak and escape with their lives, heroic adventurers must battle dark dwarves in their underground city, explore the abandoned caverns of the Elder Elves, and deal with weird alien entities from Beyond. Their goal is to stop the Master of the Twisted Caverns and his dark minions from completing his sinister plot before it's too late... if they can.

Included in this product are a 96-page adventure book detailing the dungeon that lies beneath Firestorm Peak, 4 full-color poster maps detailing all the important locations in the complex, and a sheet of 56 counters for use with the tactical maps in major combats.

For four to six characters of 5th to 8th level.