I recently ran White Plume Mountain over a weekend D&D bender for my regular play group. It's a very short and brutally designed puzzle dungeon that has a long history in D&D, one of the few modules for the original edition of the game that has been updated for damn near every edition since including 5th edition. The compilation book Tales from the Yawning Portal has seven classic adventures including of course, White Plume Mountain.
While Tales does include gorgeous new art of the mountain and updated traps and monsters it doesn't do much more besides replicate the sparse introductory text used in the original modules to try and give hooks for player characters. When White Plume Mountain was first published stories and cohesive world building wasn't something TSR thought players or DMs cared much about - or if they did they would do that on their own. Fair enough. Tales itself doesn't bother to give the DM much help bringing the adventure into Faerun, the 'default' setting for 5th edition. In fact it provides exactly one sentence:
Sounds like a tale from the yaaaaaawning portal amirite?
Being the sort of person who can't be content to not know how and why White Plume Mountain exists in Faerun instead of Greyhawk (where it was first published) I had to explain where Keraptis and his mad lair came from. So let me present to you how I would have written this section of Tales and how I made this mad adventure slot into my personal Faerun campaign.
Step 1) Re-Write the Legend
The module has always come with a "The Legend of Keraptis" page which can be given to the players to provide them with what the general hearsay about this Keraptis character is. Since this adventure is published in Tales from the Yawning Portal and the Yawning Portal is an actual tavern in Waterdeep with a great bar tender I re-wrote the Legend as if he was telling it with some extra Faerunian flavor.
Step 2) Keraptis and the Mountain in Faerun
Next I fleshed out a bit of the historical background for this wizard and where he ended up. He's supposed to be old, even the original adventure has him over a millennia old. In Faerun this lines up pretty well with the fall of Netheril, which happened to be filled with powerful wizards.
Keraptis in the Realms
Geography of the Mountain
Step 3) Re-Write the Letter
The final part that I felt needed to be updated was the poetic letter Keraptis sends to taunt the lords he has stolen from. I decided to edit some of the opening stanzas in order to hint at the location of the mountain within the mere of dead men. I have a digital hand out version with a background and a printable version with only text. Printing it on some parchment paper made a great handout at the table.
So there it is. Hopefully you have a clearer picture of how this dungeon could fit into the Forgotten Realms or maybe it sparked some ideas for how you would do it completely differently. That's the fun of Dungeon Mastering, happy gaming!