The Cave of Undolee is a powerfully charged location through natural magics. Heavily borrowing from Celtic mythology where gates between worlds open during certain times of the year, phases of the moon, or whatever schedule the GM needs to drive an adventure forward. The map itself was created when I was mapping for game night. I screwed up the map so bad, I just kept it and thought I'd create my own version of it.
The image from the 1st edition Player's Handbook (pg. 121) sticks in my mind.
For me, the Planes of Existence are layered upon one another. Sometimes sharing the same space as other planes. Places where planes overlap and conditions are right, natural gates occur. The Cave of Undolee is a gateway to the Plane of Water.
These gateways provide opportunities for gameplay beyond the normal realm of existence. With preparation, probably a few trial runs, a party could adventure in the Plane of Water. This provides complications the party has rarely come across.
In this adventure, The Cave of Undolee is a glimpse of that possibility. And if the GM chooses, could be a focal point for an 'outsider' enemy group. The sahuaghin are a fantastic enemy race that provides a new threat beyond the traditional orcs and goblins. Plus, they have that otherworldly feel, especially if a GM plays up the sahuaghin's potential for mutations. And with the threat of possible invasion, it is not like the party can track the enemy to a cavern stronghold. No. The party would need to travel to a place where the environment itself could kill them at any moment.
I have a map drawn already for an adventure in the Plane of Water. I hope to have it out next month. It'll be the first adventure that will include sharks. So I'm excited about that. It'll take place as soon as the party moves through the gate.
As always, my thanks to my patrons. Their continued support is incredible. I love creating these adventures, printing them and having them in hand. Here's to a productive December.