Compelling the PC's to an unknown destination... how?

[nameless]

One of the best hooks is to reverse a player's expectations, and usually yours at the same time.

Instead of the players going blind into the temple, maybe they are near the temple and see a strange humanoid creature of a race they have never encountered or heard of (the underground people). He could be the intrepid idiot who went against the grain to explore the surface world that he thought was lush and vivid. And was quickly hurt/maimed/bitten by a poisonous snake leaving the heroes with some further hook that something important could be underground.

Or, if you want a more hands-on approach, the kid sees the adventurers and is fearlessly curious about them. Maybe he speaks a strange language, maybe not. Maybe he has never seen something common that all the adventurers carry, and wants to trade for it. He might offer something amazing for something the adventurers take for granted, like a jewel-encrusted gold statue worth 10,000gp for a furry blanket.

Some other posters have had some good ideas that make good hooks, but take it a step further and instead of telling them they heard El Dorado is in that temple, show them hints and let them figure it out for themselves.

 

[Quartz]

How about pulling a switch on them and simply dumping them in it? They're exploring the ruin and the ground simply opens up - they fall into a sinkhole or something - and when they dust themselves down, they're in the middle of the real adventure

 

[Pbartender]

Excellent suggestions.

The only problem with that approach is that I wanted the underground city to be unknown and unheard of. The adventure starts out with the PC's investigating a newly exposed 'ruin'. Noone expects there's a whole civilization under the ruin. The inhabitatants believe the surface to be desolate and have not come to the surface in a over a thousand years.

As far as the PC's know at the start, they're just exploring a ruin for whatever reasons they come up with (for being an adventurer) at character creation. And therein lies the problem... once they discover that the whole campaign (at the start) is underground, there's nothing stopping them from returning to their hometown or wherever except the fact that I don't have any of that established! I've only fleshed out the underground city and environs.

Right... So where's the problem?

The PCs need a reason to be exploring the ruins, not the lost city. Once you get them into the ruins, it's easy enough to have them stumble upon the lost civilization.

From there, there's lots of options... Plain curiosity... Suggestions of untold wealth, knowledge or power... Getting captured by the natives... Specific links to character backgrounds (like E-R's sigil/birthmark or prohpetic dream ideas)... Whatever.

The point is, once they're exploring the ruins, introducing them to the lost civilization that's hiding within is trivial.