By Adam F Burke
The state of Nevada has one of the highest rates of homelessness in the US.
But even though there are more than 14,000 homeless people in Las Vegas, it is easy to spend a weekend in Sin City and never see signs of a crisis.
Most tourists take in Vegas from the interior of a casino - slot machines, blackjack tables, cocktail waitresses in impossibly tiny outfits.
If you are willing to pay the price of admission, a lift can transport you to more excess upstairs - rooftop pools and lavish suites.
But what if there were a lift that descended below the sunken lounges, past kitchens and utility closets, through layers of concrete, into the ground beneath the casinos?
Here, you would see another, very different, version of the city: the storm drains.
Matt O'Brien, a Las Vegas writer, has been exploring this underworld for several years. In 2007, he published a book, Beneath the Neon, about exploring the 300 miles of tunnels that criss-cross beneath the strip.
The evening I meet him, he is wearing heavy boots, and carrying a backpack and industrial-sized flashlight that could double as a weapon.
"I've been exploring these storm drains for more than five years," he says, sloshing through muck and gravel that blanket the tunnel floor.
"I think I know these storm drains better than anyone who doesn't actually live in them. And I know the storm drain system probably - and this is nothing to brag about - better than anyone else."
Just because you've been in the drain the day before, that doesn't mean it's going to be the same environment the next day
It is after 9pm on a weekday night. Above, the Vegas strip is coming to riotous life.
Gamblers are laying bets, showgirls are flourishing their feathers. Below, in utter darkness, the storm drains echo with the faint sounds of dripping water.
At one point, the tunnel widens to form a chamber. A flashlight reveals the plump, almost illegible cursive of graffiti lettering covering the walls - beautiful colours and designs.
"This is one of the underground art galleries that I discovered down in the storm drains," Mr O'Brien says.
Noises make me stop and shine the light back in the other direction.
Mr O'Brien understands this impulse.
"There's always the butterflies," he says. "There's always that apprehension when you walk into a storm drain. Just because you've been in the drain the day before, that doesn't mean it's going to be the same environment the next day.
"I've met people down in the drains - you'll come down the next day, and all of a sudden, you know, they'll tell you to screw off. They'll...make it clear they don't want to talk to you today."
Over the years, Mr O'Brien has met more than 100 people who live in the tunnels.
We head away from the trickling water, down a side channel that stays dry most of the time.
The ceiling gets lower, the corridor narrower, and the air becomes stale with the faint scent of body odour and human waste.
We come upon an encampment - a cardboard lean-to where two men are sitting in the glow of candlelight. One of them is slumped on a couch.
In front of him, on a makeshift coffee table, are a few hypodermic needles. The other man is better groomed, wearing a button-down shirt and a decent pair of trousers.
They greet Mr O'Brien enthusiastically.
Matt O'Brien still visits the tunnels, even though his book is finished
The men are introduced as Brian and Steve. They have not seen O'Brien since he was down here at Thanksgiving last year.
Steve talks about how they returned to their camp that day to find Mr O'Brien had left them Thanksgiving dinner.
"Big turkey and stuffing. It was pretty good," he says.
Steve is the well-dressed one. He is 42 and grew up in Las Vegas. He makes his living at casinos around town, doing what is known as "silver mining": looking for credits left behind on slot machines.
"You know, I'll start at Harrah's. And depending on how I feel, I'll go to either the Venetian and the Mirage. A lot depends on how I look, because those are two very hard places. If you don't look right, they'll stop you and watch you. It's always busy at Harrah's, so you're able to walk through the casino without drawing much attention to yourself."
To blend in, Steve has to dress the part.
At his "bedroom" (demarcated by cardboard walls), he has got racks of shirts and trousers. He has a queen-sized bed, a dresser, and even a makeshift shower.
Needles and bottles
Steve says his luck varies. The night before, he had visited several casinos, and things had not been going well.
"Then I went to the Bellagio. I was walking through and turned the corner in one area of the casino, and there on the machine was $116 (£70). Nobody around, so I hit the cash-out button. Took it, cashed it out, and that was the end of my night. Helped me out today. I ate very well today. I had a late breakfast last night. And I still have about 50 bucks left," he says.
But Steve is addicted to methamphetamine and gambling, so holding on to money can be difficult.
"That's what I'm trying not to do is gamble my money away any more. And as far as the drugs, I'm trying to slowly get myself to where I don't crave it," he says.
"Tonight, I'm taking it easy. I figure I'll just call it an early night and see what I can do tomorrow," he says.
There are certain things about underground Vegas that I prefer to above ground Vegas
After a while in the Las Vegas storm drains, it is easy to lose one's bearings - to forget that directly above is a very different world.
"You can be in the Hard Rock Casino, which is one of the hipper, kind of younger, richer casinos in town, kind of celebrity-watching people, people-watching, betting $1,000 per hand in a game of blackjack. And right underneath the Hard Rock is one of the worst Skid Rows I've ever seen in my life," Mr O'Brien says.
There are broken bottles, hypodermic needles strewn all over the tunnel floor and people passed out.
"And last time I was down there, I actually saw some blankets and teddy bears and stuff, which gave me the impression that a young kid was living down in there with a mom or dad, or both."
That contrast is what keeps Mr O'Brien coming back to the tunnels.
He brings food and clothing to people like Brian and Steve. The tunnels have become a kind of refuge for him from the city.
"When work wasn't going all that great, or my relationship with my girlfriend wasn't that great, I would strap on the boots and grab my flashlight, my gear in the trunk. And a lot of times I would just gear up and walk a tunnel," he tells me.
"In some ways, there are certain things about underground Vegas that I prefer to above ground Vegas."