People 'losing their minds' after finding out what was inside London's O2 Arena before it become a music venue

We think we know about everything until we don't. And now the London's O2 Arena can officially enter the realm of unknown knowledge.

If you're a millennial like myself and born in the first half of the 1990s, you'll probably remember the famous London landmark opening its doors for the first time on 31 December, 1999.

Back then it was a very, very different beast. And it would be around eight years until it opened as a concert area that we know it as today.

The modern day O2 Arena in London. (Getty Stock Image)

Instead of some of the best music acts in the world entertaining thousands of spectators on a weekly basis, the crowd couldn't have been different.

Enter the Millennium Dome. And with that countless Gen Z types going 'what?'.

Plans to build the structure began way back in 1994 with Tony Blair getting the project under way in 1997 after he became prime minister, which cost £789 million (£1.45 billion in modern money).

But it is in 2024 that the dome is going viral over on X (previously Twitter) as thousands come across its original purpose for the first time.

One X user wrote: "Just finding out what used to be inside the O2 Arena before it was an arena and I’m losing my mind, what?"

Another posted: "WHAT?????? THE HELL??? IS THIS??"

The middle of the Millennium Dome, which is now the O2 Arena. (Steve Eason/Hulton Archive/Getty Images)

Some eight years before gigs began, the venue's Millennium Dome period began by welcoming in the new millennium through a major exhibition celebrating the start of the year 2000.

It was all very meta, with 14 exhibition zones for people to walk through including Body, Work, Money, Play, Talk, and Rest.

We're not making it up; this was the Body zone:

The Body Zone at the Millennium Dome. (Richard Baker / In Pictures via Getty Images Images)

There were also a number of memorable and unique sculptures on display, including a giant boy crouched down wearing nothing but what look like boxer briefs.

Millions visited the site; albeit half of the expected crowds with six-and-a-half million walking through its metaphorical dome doors.

And it then closed exactly a year after opening, with it no longer open to the public after 31 December, 2000. Reports said it was costing £1 million a month to stay open.

With unique images of the exhibits going viral on X, those who remember the exhibit pre-O2 days have been left a little bruised by the realisation of their age.

The Millennium Dome. (Getty Images/Carlos Lopez-Barillas/Liaison)

"Visibly ageing at the news there are people who aren't aware of the existence of the Millennium Dome," one X user posted.

Another said: "Never thought I'd be into that generational divide shit but this is ridiculous. How dare you make me feel this old, kid. Get off my lawn."

And a third joked: "People don't understand that a lot of British culture in the New Labour years was like the Willy Wonka Experience on an unlimited budget."

The official O2 account then posted: "You're welcome everyone."