Very simple idea. Two Obsidian Portals generated as terrain on the map. Units ending on the Portal may pass from one to the other.

I think it's a great idea, either as a unique improvement or as rare result from exploring layers!
Regards.

Or perhaps an improvement for the sheaim with a limit on number.

I think this is a great idea. could add interesting dynamics to a game. Although it may be over powered if the sheaim could build them... Maybe have a sheaim specific wonder where they connect into those other two gates giving them access to go to either of the 2 gates. -req divination maybe?

Pass through the Ether (sp?) or Strength of Will sounds better. Nothing earlier than Arcane Lore at least. Divination is way too early.

@Zup you may be right. However, early travel isn't a big advantage when the gates travel to 2 random places on the map (and the origional idea would benifit whoever builds next to one of these gates anyways without a tech). Its a different story when you can build gates in cities and have a clear tactical advantage.

I figured they could be a remnant of a bygone Nexus wonder from before the Age of Ice. To ensure they are a little more useful, the mapscript could be used to ensure that they are a minimum of X tiles apart, where X is dependent on the map size.

Also, any city with an Obsidian Gate within it's fat cross could receive +1 Trade Route.