Without premeditation or intent, I made one of my players take an interest in one of my campaign world's aspect.
To be more precise, he's taken a keen interest on the campaign specific calendar. It was not my intention to hook him onto it like that, but I introduced into the campaign a magical item that is tied to the phases of the three moons of the game world.
It started when I vaguely remembered something in the Savage World's Fantasy Companion about Grimoires. I wanted the Druid in my campaign to gain access to more powers without the need to wait for level-ups. So I cracked open the SWFC and found the reference to Grimoires and how they can allow a spell caster to gain new powers without taking the New Power edge every time.
But he's a Druid and I felt like a more oral method of transmitting the knowledge and wisdom was more appropriate. So I simply applied a Trapping to the Grimoire. Instead of finding a musty old tome or delicate scrolls, he found Leylana's River Stones. Five smooth stones with swirling designs and runes upon them in a supple doe-skin pouch. After doing some research, he discovered that when placed in a stream of clean water or a basin filled with pure water, under one of the many lunar alignments, the image of Leylana would appear and she would impart her wisdom upon the applicant. As of this writing, the last time the Druid used the Stones was a minor alignment, so I had Leylana impart some esoteric druidic knowledge that will give him a +2 on an appropriate Knowledge check in the future (nothing specific, I'll just let the player tell me he heard this from his mentor when it comes up).
In the world of Shaintar, there are three moons and 16 months, and there are many possible lunar alignments possible. So now my friend Marc has made himself a copy of the calendar and keeps track of time that goes by in game.
He could've simply asked once in a while if the moons would be aligned and I could've just hand waved it and moved on. But he has taken interest and I'm encouraging it. It makes me even more aware of the passage of time in game and I'm also more motivated to keep track of it. Especially since they are currently on an important mission that is also time sensitive. They must hurry before the Gates of Hell open.
Have any players of yours taken a keener interest in your campaign world somehow. Maybe a calendar, special events, places or businesses, etc, and that you hadn't planned on but it somehow made the game seem more alive for them, more engaging?