Imagine this scenario. A group of tourists is in New York City near the 9/11 memorial. They are laughing and taking selfies near the edge. Then they cross an invisible line, stepping onto the plaza where the names are carved, and everything changes. Voices drop to whispers. Phones go away. Bodies slow down.

No fence stops them. No sign commands silence. Yet everyone knows: this ground is different.

That's sacred space at work.