In 1991, TSR published the module named FA2: Nightmare Keep with the module code “FA2”. It was written by Rick Swan and illustrated by Valerie Valusek and Terry Dykstra with the cover art illustrated by Gerald Brom. This 64-page booklet had an outer folder containing encounter tables and fold-out maps. The adventure was designed as an ultimate death-trap dungeon, for groups bored with adventures like S1: Tomb of Horrors.
This "FA2 Nightmare Keep" conversion guide allows DMs to run the original module with 5th edition rules. Also included is a handy reference sheet for encounters, hazards, and traps. To use this conversion guide you will need a copy of FA2: Nightmare Keep, originally available as a hard-copy and now for sale in digital and softcover formats.
Four of the magic items and 17 of the monsters have been converted to 5e standards, while all other magic items and monsters that exist in the module which are already found in the 5e core rulebooks are annotated with the page numbers which they can be found or what substitutions can be made.