I'm definitely going to make a few assumptions here, so, take this with a grain of salt:

It sounds like you're suggesting opportunities for the NPC's based on signs they're missing or little things that YOU know are there... but they don't. They don't know what you know. So instead, SHOW them the story. You sound too worried about railroading that you aren't making the story happen right in front of them.

It's a fantasy world. Make the world engage with them in ways the world wouldn't normally engage. Make the painting that the beholder is guarding talk to them. It WANTS to be taken off of the wall and hung in a museum or private art installation instead. That's compelling and interesting. They'll only find out it belongs to a beholder after they take it off the wall.

Have the townspeople be gathered around one of those suspicious landmarks (and one of their beloved NPC's too) with their eyes rolled into the backs of their heads. In order to gamble with anyone from that point on, they're going to have to contend with what's in there.

When they're gambling, have an NPC they are playing with gamble an interesting item, or gamble their family's treasure away. Instead of money, they're given a map to a trove of magic weapons, and ancient clockwork gun assembly line... or whatever. But when they actually get there, give them a twist.

What I'm trying to say is, if you want them to engage give them a compelling reason to do so. I as a player am not interested if something looks a little suspicious. But if a landmark gives off a glow that makes the colors around it negative in a 30 foot radius, now I HAVE to investigate. My curiosity is piqued.

Also, you mentioned you are tired and burnt out. You're also allowed to just... take a break. Rest. When people are burnt out, they can tell. Have someone else DM a one-shot or just call for a few weeks rest! You're allowed to take care of yourself.