In a vast, dark room, the lights glow a steady green, blue, yellow. I'm not inside the Matrix, but it's not far off.

With every step, I walk past thousands upon thousands of virtual interactions between real people happening through the world's largest social network, Facebook.

I'm inside the company's newest European data center in Clonee, Ireland, a small town on the fringes of Dublin. It's one of a spiderweb of facilities across the US and Europe and one of the rare places you can say the social network exists in a tangible form.

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"The brain of the internet, of Facebook, sits here," says Niall McEntegart, Facebook's data center operations director for Europe, as we walk between flashing server stacks.

These massive facilities provide the foundation for a system that can quickly ferry every like or comment from the nearly 1.5 billion people who log in each day around the world and throughout the massive social network. And that's before you account for the millions also using other Facebook-owned products, including WhatsApp and Instagram. Facebook CEO Mark Zuckerberg may have to battle claims of political bias and fend off trolls and propaganda machines, but those issues are inconsequential to these monolithic structures.

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I got a rare opportunity to explore the inside of the newly opened Clonee site to see what makes it tick.

Pizza boxes and spaghetti loops

Facebook broke ground on the Clonee data center in 2016, and with a third building still under construction, the facility won't be complete until the end of next year. But it is operational, with eight data halls, each around the size of a soccer pitch, already running.

We pass from one dark, high-ceilinged room to another, each protected by biometric fingerprint sensors, and clatter up and down metal stairways. With little human presence, it feels like actually walking around inside a giant computer. As we set out I'm warned about tying my hair and scarf back to stop them catching in the fans or coming into contact with any high-voltage electricity. "It's perfectly safe," says McEntegart. "As long as you don't... do anything."

Inside there's so much free space that it does feel very safe, even for a klutz like me. Someone has made tying up the 200,000 kilometers of fiber cables -- enough to wrap around the world five times -- look like the work of a minimalist neat freak. There's even order to the yellow cables draping down from server racks: They're looped around artfully like fresh spaghetti hung up to dry.

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Making my way down an aisle, I notice some of the server stacks are marked "feed" to signify that they are powering Facebook's News Feed. It's impossible to know exactly how many people are interacting with the piece of technology in front of me right now, or what they're each asking of it -- liking, commenting or just getting lost in the endless scroll.

I briefly wonder what would happen if I tugged on one of the wires feeding into one of the machines -- how many glitches I'd cause, how many people it would affect. I didn't, of course.

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Not that it would've mattered. They're designed so engineers can pull them out and replace them within the space of 20 seconds. All the technology here and in Facebook's other data centers around the world was designed by the company from the ground up and is available to study, or borrow or copy via the Open Compute Project.

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I can't help but notice that sandwiched in the racks along all the row are a bunch of cardboard boxes, which seem… surprisingly low-tech in the context. McEntegart explains it's a simple hack to stop air going through, preventing waste energy. It also allows the Facebook workers to build out and add to the server whenever they want. He slides one of the boxes out for me to take a closer look.

"What do you think we call them?" he asks, proffering it to me with a glint in his eye.

The answer seems immediately obvious. "Pizza boxes?" I ask.

"Pizza boxes," he says with a grin and nod. I have to stand close to him to hear him speak. The constant, powerful rumble of the servers sounds like the hum of a thousand cicadas.

A hive of activity

Outside, it's a different story -- here the buzzing of insects is all too real. All around the grounds of the data center are beehives, painted Facebook blue and with letters spelling out the company's name. The splash of color contrasts with the very gray, very boxy machines inside.

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The addition of the beehives, which house around half a million bees in total, to the Clonee data center serves multiple purposes. First, they're part of landscaping efforts that aim to pay homage to the wider community. The grounds take various design cues from Irish heritage sites -- the earth mounds, for example, have been formulated to echo the Hill of Tara. But this extends to the inclusion of local flora and fauna, with the hives surrounded by bursts of colorful wildflowers.

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Second, the bees are a natural fit for Facebook's sustainability mission. There's no one I meet at Clonee who, when I mention the hives, doesn't come at me with fistfuls of statistics about the declining global bee population. And their passion is more than academic. In spite of having trained beekeepers on staff, more than 20 employees (out of around 300) at the data center now voluntarily contribute to maintaining the hives. Some including McEntegart, have also started to keep bees at home. The honey, which he says is "absolutely delicious," is served in the data center canteen.

In the reception area are lemon trees, colorful murals and high-backed millennial pink armchairs. A pride sign is emblazoned on one wall within the office area that joins two of the server halls together, echoing the one currently on display at Facebook's engineering office in London.

It's easy being green on the Emerald Isle

Unlike other non-US Facebook offices where you'll hear at least a few American voices in the mix, Irish accents abound here, demonstrating that Facebook is committed to hiring local staff. In fact, the talent in Ireland is one of the reasons Facebook even has data centers here, McEntegart says. That and the stable, temperate climate that makes it easy to keep the servers cool. The favorable tax climate that's persuaded Facebook and Apple to keep their European HQs in Ireland also seems like a strong incentive, although McEntegart denies that this is a factor when deciding data center locations.

It also helps that Ireland (along with Scotland, just a short hop across the Irish Sea) is one of the best sources of wind power in the world. The data center is fully supplied by renewable energy -- mostly by wind power supplied locally from onshore or offshore wind farms.

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For Facebook, this is yet another step in its pledge for the company to completely run on renewable energy by 2020 (something that Apple already boasts of). The company doesn't own any wind farms itself, but has strong partnerships with companies that do.

I climb onto the flat top of the data center to observe the cabinets containing the cooling system. This pumps cool air down into the server halls below, and takes in the waste heat that rises back up, converting it into energy. It's about twice as efficient as most other cooling systems out there, says McEntegart.

Back in the server halls, I pass through a door that leads to an aisle between rows of servers. The transition leads me from being slightly chilly to feeling like my whole body is being gently buffeted by a hair dryer on the medium-warm setting. Here's where the hot air gathers before being sucked back into the cooling system above.

The system works perfectly as long as it doesn't go above 29.4 degrees Celsius (84.9 degrees Fahrenheit0, says McEntegart. After that they have to tap into more traditional water cooling. This is unlikely though -- we're in Ireland after all.

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He can't tell me what proportion of computing power Clonee contributes to Facebook globally, but seeing all this -- the size of the facility and infrastructure, its stability, the way that it's just one part of a global network -- is a reminder of the power of Facebook.

Facebook's portfolio of products and apps -- Instagram, Messenger, WhatsApp and Facebook itself -- could easily change over time. But as long as Facebook owns these centers, the brains of the system will remain here in a small town in Ireland, and other small towns around the world, buzz, buz,z buzzing away.

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