To the London Mithraeum last Friday. Removed from its previous post-war incongruous location at ground level in the heart of the City of London, and unavailable for some years, it has now been returned to its subterranean location on the banks of the now-sunken river Walbrook. An excellent piece about the reconstruction here. I've visited many Mithraea over the years, some of the most atmospheric in Rome, at San Clemente for example - see here.
I think the newly-restored London temple has managed to conjure up the numinous atmosphere of the all-male congregation chanting in Latin before the stone image (now in the Museum of London) of the tauroctony very effectively with sensitive lighting, sound and smoke. There is also a very well-displayed array of finds from the site of the new Bloomberg building, beneath which the temple now sits. The guide told me that 80% of what you see is original, the side walls are much higher than I remember them from the original and make it more impressive. Entry is free, but you have to book in advance - see here.
Author of Subterranean City, Beneath the Streets of London, London's Coffee Houses, Decadent London, The Folklore of London, Subterranean City (Revised and Expanded Edition), Netherwood, Last Resort of Aleister Crowley, Lord of Strange Deaths, the Fiendish World of Sax Rohmer; Secret Tunnels in England, Folklore and Fact