Get a free D&D adventure based on a classic dungeon crawl on DND Beyond
Wizards of the Coast's upcoming D&D book Quests from the Infinite Staircase will remix six old school adventures from the days of Advanced Dungeons & Dragons 1st Edition, including Expedition to the Barrier Peaks and The Lost Caverns of Tsojcanth. The latter is also being made available in an abbreviated form called Descent into the Lost Caverns of Tsojcanth, and you can currently claim it for free on DND Beyond.
First published in 1982, The Lost Caverns of Tsojcanth began life as a tournament module run by D&D co-creator Gary Gygax six years prior. A competitive one-shot explicitly designed to kill the characters players brought with them to convention games, it remained unforgiving even in its modified, published form. A lovely document of this is Jason Thompson's comic-style walkthrough map of the module, which has one of the party members crushed to death by rocks before even making it to the dungeon—a common occurrence back in the day.
Tsojcanth was just another dungeon crawl in both of those incarnations, but it was notable for the amount of new monsters it added to D&D like the water weird, behir, marid, and derro, as well as various demon princes like Graz'zt and Baphomet, which remain part of the D&D bestiary to this day. If you're interested in the topic, here's more on the origins of D&D's odder creatures, specifically the ones you'll meet in Baldur's Gate 3.
Quests from the Infinite Staircase transforms these old adventures into a new campaign linked by a series of doors accessed via the Infinite Staircase—a multiversal travelator first detailed in the Planescape campaign setting. In the new adventure anthology, player-characters are recruited by a genie named Nafas, who uses heroes to help him fulfill wishes in various worlds. It's designed so the scenarios can be run individually if you prefer, or as a linked campaign that takes characters from level 1 up to level 13, and should be out on July 16.