Last week I went to see Chord, an installation by Conrad Shawcross in Kingsway Tram Tunnel. It was an intriguing experience, a chance to explore a small fragment of London’s forgotten subterranea. Here are some snaps I took on my phone; just the tunnel (the miraculous artwork itself can be seen at Londonist and elsewhere). Arts organisation Measure deserve praise for putting the project together, as do Camden Council for letting them take over the Tunnel, which they normally use for storage.
Tom Chivers 
What you describue as miraculous, I must go to see.