Peering over people’s shoulders, I could see that the mouth of the tunnel was capped with a knee-high structure like a small well, built of dark reef-rock or heavy-duty biopolymer, with an iris seal which had been wrenched open. The winch, a few meters away, seemed monstrous now – far too large and industrial-looking to be involved in any light-hearted sport. The cable was thicker than I’d expected; I thought of trying to estimate its total length, but the sides of the drum concealed the number of layers wrapped around it. The motor itself was silent except for the hiss of air across magnetic bearings, but the cable squeaked against itself as it spooled onto the drum, and the gantry creaked as the cable slid over the pulley.

No one spoke. It didn’t seem like the time to start asking questions.

Suddenly I heard a gasping sound, almost a sobbing. There was a buzz of excitement, and everyone craned forward expectantly. A woman emerged from the tunnel, clinging tightly to the cable, scuba tanks strapped to her back, face mask pulled up onto her forehead. She was wet, but not dripping – so the water had to be some way down.

The winch stopped. The woman unhooked a safety line linking the scuba harness to the cable; people reached out to help her onto the lip of the well, and then the ground. I stepped forward, and saw a small circular platform – a coarse grid of plastic tubes – on which she’d been standing. There was also a twin-beam lantern fixed to the cable, about a meter and a half above the platform.

The woman seemed dazed. She walked some distance away from the group, almost staggering, then sat down on the rock and stared up at the sky, still breathless. Then she removed the tanks and mask, slowly and methodically, and lay down on her back. She closed her eyes and stretched out her arms, palms down, spreading her fingers on the ground.

A man and two teenage girls had separated from the others; they stood nearby, watching the woman anxiously. I was beginning to wonder if she needed medical attention – and I was on the verge of discreetly asking Sisyphus to refresh my memory on heart attack symptoms and emergency first aid – when she sprung to her feet, smiling radiantly. She began to speak excitedly to her family, in what I took to be a Polynesian language; I didn’t understand a word she said, but she sounded elated.

The tension vanished, and everyone began laughing and talking. Munroe turned to me. “There are eight people in the queue ahead of you – but it’s worth waiting for, I promise.”

“I don’t know. Whatever’s down there, my insurance doesn’t cover it.”

“I doubt your insurance covers a tram ride, on Stateless.”