In one of my old homebrew worlds, the central religious feature was a tall unfinished tower. Its construction was begun long ago in a rare age of peace, when all the humanoid peoples of the world came together for one purpose. They planned to build it tall enough to reach the heavens and grant them entry into the realm of the gods.
Of course the gods didn't like that idea. One day they sent a great omen to all the people of the world, warning of tremendous destruction and woe if they continued on their path.
Unlike the builders in a similar old story, these people actually listened, and abandoned construction of the tower. That's why all people in that world spoke a single language (which D&D calls "Common"), rather than being split up into national and regional tongues. The half-finished stump of the tower was left in place, as a reminder that mortals shouldn't challenge the gods.
I don't think I ever actually managed to run a campaign in that world. I should dig out my notes again, it would work really well with 3E.