In the book's final chapter, Nurse suggests the children visit the "Egyptian Hall, England's Home of Mystery." She gives directions - superfluously for the children, but usefully for the posterior reader (which is I suppose what we who live in posterity must be):
"It's in Piccadilly, [...] not so very far down on the left from the Circus. There's big pillars outside, something like Carter's seed place in Holborn, as used to be Day and Martin's blacking when I was a gell. And something like Euston Station, only not so big."
"Yes, I know," said everybody.
Except that they don't know, because when they get to the Egyptian Hall they find it's been torn down, and that "England's Mysteries are now appropriately enough enacted at St George's Hall", in Langham Place. This is a very topical reference: the Egyptian Hall became defunct only in 1905, just a year before the book was published. Was it a late edit, necessitated by that news? Or was Nesbit making an Ozymandian point about the transience of earthly magnificence - which would certainly fit the theme of the book, which has shown the destruction of Atlantis only a couple of chapters earlier?
Luckily, however, photographers and artists haves preserved these rather Egyptian-looking buildings for our pleasure:
The Egyptian Hall:
Day and Martin's blacking:
I assume this building (on High Holborn) is no longer extant, though there's a similar one here, looking if possible even grander:
Was it really in such a place as this that the young Dickens pasted labels onto bottles of boot blacking? It's not how I imagine early nineteenth-century factories!
This survived longer than the rest, but was demolished in the '60s despite the best efforts of John Betjeman - mostly I think (as was once said of Walter Ralegh) for "being left over from the previous reign".
And St George's Hall:
No outside view this time, but here's St George's Hall from the inside, where the children eventually watch David Devant perform his conjuring show. I think it's now the site of the BBC Broadcasting House, which seems very appropriate for England's Mysteries. Today, however, they're caught in the act of playing Hamlet: