From publisher blurb:
This supplement features an immense Gygaxian OSR random dungeon generator system, crammed into 83 pages. It’s focused on empowering you to create the sprawling level 1 of any mega-dungeon, or any smaller dungeon set to challenge adventurers of experience levels 1 to 3. The challenge levels of the monsters, traps, tricks, and treasures all reflect that difficulty level. You can use this book to design any number of dungeons, and if your group is patient you can even use it during play. You will also find some experimental solitaire rules here, if you like to practice the dungeon crawling yourself! This book’s systems interlock with the Classic Dungeon Design Guide series (CDDG1-3) as well as the Book of Dungeon Traps (BDT1) if you want to add more detail to any aspect of the design.
The system is comprised of many branching D100 and D1000 tables. Sub-systems are provided to generate:  starting areas,  random doorways,  corridors,  dead ends,  level connectors (stairs etc.),  unusual level connectors (teleporters, slides, etc.),  monster lairs,  monster-guarded treasures,  room size and dimensions,  room exits,  unusual doors,  room contents (lair, trap, trick, etc.),  side passages,  traps,  tricks (a full 17-page system with millions of potential results), and  unguarded treasure hoards. At the end you’ll find an Appendix with troubleshooting and solitaire advice, and a quick reference hyperlink section which will allow you to flip through the tables quickly.