Yet people are overwhelmingly having fun. They spin around, strike ballet poses and make snow angels on the ground, then whip out smartphones to capture the imprint.

The more fun you want to have, the more you have to step into the light.

The floor is lighter in several areas, which create more snapshots of your movements. People gravitate toward them. The more fun you want to have, the more you have to step into the light.

The juxtaposition of an imposing environment with carefree enjoyment is disconcerting but understandable. While visitors share the pervasive feeling of being watched, they don't know who's watching, or to what ends. It's hard to care. Besides, everyone else is consenting to being monitored too, and look at the fun they're having.

This is the heart of the installation: how we trade our privacy for fun.

"We also are actively involved in this," said Jacques Herzog on a panel at the installation's opening. "It's not just that we are victims."

Every time we use services like Instagram or Snapchat, we voluntarily give up our data in exchange for entertainment. The more we give -- adding geolocation, tagging friends, linking other social media accounts -- the more we're rewarded with interesting features.

Sometimes the nefarious ways our data is used comes to light -- advertisers used to be able to exclude Facebook users on "ethnic affinity," and Uber bought anonymized Lyft receipts pulled from the email inboxes of Unroll.me customers. But for the most part, the knowledge of what personal information we're giving up is hazy.

A post shared by Ai Weiwei (@aiww) on June 6, 2017, at 10:18 p.m. PDT

"As a New Yorker, or somebody in the city, you expose yourself to surveillance all the time, no matter where you go," said Ai Weiwei at the panel. "Even if we know there's a camera there, we don't even know what is being recorded and how later [it] would become something which is useful."

Ai knows these issues intimately. While Hansel & Gretel uses surveillance for fun, the iconoclastic artist has also made fun of surveillance. In 2012, while under state monitoring in Beijing, he wryly broadcast four live webcams from his house to weiweicam.com until the government shut it down in less than two days.

While we seldom get a peek behind the panopticon, the second part of Hansel & Gretel provides the viewpoint of the person doing the watching. In a separate area, visitors use iPads to watch feeds from the security cameras, drones and infrared cameras following those in the main hall. They can take a picture of themselves and facial recognition will identify grainy photos of them wandering the building earlier.

"The first part was physically disconcerting -- I couldn't see where I was walking," said Yvonne Caruthers, a fellow visitor. "The second part was alarming."

Yet, like tech companies, the exhibit made public only a sliver of the insights they potentially could have harvested. With all that motion tracking and video footage, perhaps other inferences could be made: who a visitor interacts with, how rapidly they move through the exhibit, which areas they spend the most time in. If the exhibit showed people just how much big data thinks it knows about them, the cost of their earlier fun would be more apparent.