Every Palace a Prison
Art by: Rima Salloum
I've done this before, a mid adventure challenge for the players. I'll provide them a novel environment where they have a chance to do, just about whatever they want, for as long as they want to see if they forget about the task at hand.
After a few days of slaying monsters and crawling into dark caves, we might all want to unwind a bit. Enter an invitation from the Duke of Gustavus who is having an all weekend rager. A party to put Gatsby to shame! Plus they have a hot tub.
The whole scene shouldn't take very long to role-play, just let the players know that exciting events are happening that do not concern the main quest line or anybody who needs help, and don't remind them about it. There will be consequences for procrastinating too long, but it isn't your job as a GM to remind them of this.
I've once had players explore a library for an hour and half of real time. They would just open a book and I would have to think on the spot what the books contents were and what it said as they read it. They even started chatting it up with the librarian. This hour and half of real time was really only maybe 20 minutes in the game world, but the players had fun poking around, and they reminded themselves what they really wanted to do.
Interestingly enough we played that game in a real library, and if they had spent 4 hours pretendint o flip through books I might have penalized them for that.