Special level (NetHack: The Next Generation)
The School, located between levels 8 and 12 of Gehennom, contains teachers, pupils, and a principal. It has an 80% chance of being generated.
The Computer Level
The Computer Level, located between levels 8 and 12 of Gehennom, contains several hostile computers. In NHTNG, this is also the only place where certain (mostly nonfunctional) objects will appear. It has an 80% chance of being generated.
The Key Level, located between levels 5 and 9 of Gehennom, is the home of the nymph queen, the guardian of the Key of Access, which can be invoked to branchport. It also contains numerous nymphs and leprechauns, all generated awake. It has an 80% chance of being generated.
The Dragon Level, located between levels 1 and 5 of Gehennom, is the home of the Dragon Lord, who drops an artifact set of dragon scales which can be invoked for a breath attack. It has an 60% chance of being generated.
In SlashTHEM the Dragon Lord appears in the Wyrm Caves.
The Hitchhiker's Level
The Hitchhiker's Level, located one to two levels above Medusa's Island, is a tribute to Douglas Adams and his Hitchhiker's Guide to the Galaxy series. It contains a number of monsters that represent characters from the series or otherwise allude to it.
Spoiler by Sebastian Klein