It’s so beautifully produced that you won’t realize until you’re back out on the street how slight the whole thing was. In the middle 3rrd century, Romans built a temple to Mithraism, a male-only religion now lost to time. The foundational ruins of the temple were lost, too, until 1954, when construction unearthed them. Moved twice since then, they’re now displayed a few meters from where they started in what’s now the sub-basement of 2017’s Bloomberg London building. You’re admitted by appointment in groups of around a dozen, shown a wall of some 600 Roman artifacts found here (and given a tablet, but not the time, to read all the overly simplified captions for them all), then brought downstairs, where the recorded super-elocution of Joanna Lumley prepares you for the ruins themselves, which you finally see for five minutes in the last stage, the “experience.” That’s when you stand on a catwalk around the rocks and they’re ingeniously lit with scrims of powerful light and you hear voices that simulate what a ceremony to Mithras might have been like. It’s all just a theatrical new way to make a ruin interesting. In truth, we barely know a thing about what happened here. But it’s presented with artistry, forethought, and a ton of money, and it’s a rare tangible reminder of a history that goes back two millennia right where you stand.