Free Roman Temple Under Bloomberg HQ in the City

There's a Roman temple sitting seven metres under the City of London right now, and you can walk through it for free. It's the London Mithraeum, a 2,000-year-old shrine to the god Mithras that Bloomberg uncovered when they were building their offices, then decided to leave exactly where it was and turn it into a public exhibition. The whole thing's immersive, atmospheric, and honestly a bit mad.

What you get

Free entry. That's it, no hidden fees, no upsell, nothing. You get timed-slot access to the Mithraeum itself, which sits in its original position underneath 12 Walbrook, London EC4N 8DQ (postcode matters for your sat nav). Opening hours are Wednesday–Saturday, 10:00–17:00 (last entry 16:30). The nearest tubes are Cannon Street or Bank, both about a five-minute walk. You're looking at roughly 45 minutes to an hour inside, depending on how long you spend reading the Roman writing tablets and taking photos.

How to get it

1. Head to londonmithraeum.com and pick your date and time slot. 2. You've got to book as a group, minimum two people, maximum 12. Solo visits aren't an option here. 3. Enter your details, confirm the booking. You'll get a reference number. 4. Show up five minutes early. They're strict about timing because the next group's already booked in. 5. That's it. Walk downstairs, get immersed, leave when your slot ends.

What the TikTok didn't mention

• Best time to go: Weekday slots are less rammed than Saturday mornings. If you're going with mates, pick a Wednesday or Thursday afternoon, you'll actually hear the Latin chants without someone's phone going off.
• The atmosphere's the real deal: They've done this properly. Dry ice, moody lighting, actual Roman artefacts displayed where they were found. It's not a museum experience, it's more like stepping into something that's been underground for two millennia. The 400+ writing tablets include London's earliest financial document, which is properly mental if you're into that sort of thing.
• Combine it with something nearby: The Mithraeum's in the heart of the financial district, so it's not surrounded by great food. But Cannon Street has decent pubs within five minutes, and the walk to the Thames is walkable. Grab lunch after, not before, you don't want to be full going underground.

The catch

Slots book out, especially on weekends. You can't just rock up, it's advance booking only, and popular times disappear fast. Also, group-only entry means if you're a solo traveller, you'll need to find at least one other person or join a public tour (which only run April through November, so they're seasonal).

This is the best free thing in the City that nobody knows about yet, and it won't stay that way for long.