Downstairs again, at timed intervals, hence the need to book a ticket, is the temple itself. You enter in the dark. Its slowly revealed clever lighting and subtle smoke effects, along with the soundtrack of voices and chanting, attempts to create something of the cult experience.
It's mysterious and slightly shivery, and was just the perfect thing to explore on a freezing day.
To get your glimpse, book a litter to Walbrook. No denari required.