I am looking to run an old D&D 3.5 adventure. I have never played D&D 3.5 so I am unaware of the level scaling for player characters.
The book states it is for 18th level adventurers; however, that was D&D 3.5. I have a decent understanding of 5e but nothing for 3.5 and thus had to homebrew the creatures based off of some info I know from other people as well as similar monsters from around that area.
I feel 18th level 5e would be too easy, for what I have read of this module and the numbers I am seeing, this is meant to be a hard module - 6 players of 18th level and most Encounters are denoted as EL (Encounter Level) 24+. Whist we love a difficult combat that burns most spell slots and takes a whole session to burn though, having that every session would ruin the fun.
The adventure is The Lich-Queen's Beloved.