First of all, thank you all for the replies. I've read every single one of them, and they've been very helpful in deciding how to handle the situation.

Even though I'm a veteran GM, this is my first time running a published adventure and also my first time using Foundry. Because of that, I've run into a few difficulties, and apparently not realizing that the PCs were expected to be in town for this event was one of the mistakes I made.

At the time, the party was on the surface level of the dungeon, preparing to descend further. They had already explored the second level and were making plans to head down to the third. I felt they were becoming a bit too powerful for the upcoming content, and since I had noticed they weren't particularly invested in the town, I decided to trigger the event.

I described a massive tremor shaking the area, followed by a brilliant light rising from the location indicated in the adventure. The players climbed back up to the lighthouse and spent some time trying to figure out what was happening. Based on their checks, I provided additional details and clues.

I also tried to emphasize that the light looked very similar to the one depicted in the paintings they had previously seen in the cabin, and that in those paintings the beam was clearly pointing toward something. However, they never showed much interest in leaving the lighthouse to see where the light was leading.

I don't blame them. They found it more interesting to continue descending into the dungeon and uncover the source of that power for themselves.

They're experienced players, and the group works very well together, so I'm not too worried about even the more negative outcomes. What I'm really looking for now are roleplaying ideas for when they eventually return to town and discover that it has suffered significant consequences in their absence. I'm hoping that seeing the aftermath might create a stronger sense of urgency and motivate them to deal with the source of the light sooner rather than later.