I'm heading right into the GM Advice section because this kind of adventure is something I put on the top shelf of my GMing techniques. Develop a peripheral NPC, one the party interacts with minimally or maybe strikes up a friendship. Have the NPC come and go a couple of times. Build a pattern. Then drop this adventure on them.
While you can use this adventure as a straight shot, it is more effective and meaningful to play the 'long con' on the players. Get them at least minimally motivated. You'll know when you have them if after you tell the party that Amos hasn't shown for his usual drop off times, maybe Amos was bringing one of the players a gift, and they go hunting for him without asking how much or what's in it for them. A friend is in trouble. So they act.
Developing NPC relationship is something of a skill, especially in longer campaigns. And when I wrote this adventure I was thinking of it as an adventure in an on-going campaign, not so much a one-shot. There is something satisfying about getting a party of adventurers to act unselfishly. To come to the aid of a friend or a village or family without wondering how it will increase their power. An act that develops their character, to maintain that relationship that is important to them. If you can do that, you are a hell of a GM.
I took a different point of view with the map and used muted colors. I wanted to portray a 'spookier' atmosphere. I imagine the the area around the cavern, quiet. Maybe a mysterious noise of some unseen creature in the distance. The worn markers look like gravestones, but are nothing more than ancient road markers. A dark cavern with glistening wet walls. The water drops falling from the overhanging stalactites, occasionally one of the freezing drops catches a character on the neck.
Then the fall, as piercers silently drop. One after the other. A rain of deadly stone. Quiet except for the whimpering and cries of those who remain alive. The water continues to drip and the cavern's silence, indifferent.
I do hope you enjoy the adventure and find a place for it in your game. Please let me know what you think if you have the time. Good or bad. I've got thick skin so if you have a complaint or suggestion please let me know. Feedback is welcome here. Always will be.
Thank you to my great patrons. I say this a lot, but you guys and gals make this fun.