This week’s Long Now seminar was a bit unusual. The talk was given by The UX — a clandestine Paris group who occupy, conserve and occasionally repair non-visible historic sites in in the city — mainly underground. They gave a presentation to show two of their projects which people have found out about (it became clear later in the evening that they’ve done lots of projects that nobody knows about) — the underground cinema and the secret restoration of the clock on the Pantheon.

The UX aren’t alone. In London, there are the people who documented the Royal Mail railway under the city and I also met some of the team who documented the Mothball Fleet in California. It was them who told me what’s in the big covered dry dock on Treasure Island in San Francisco Bay (pictured above) that me and Ivo spotted a few weeks ago. It turns out it’s even more spectacular than we imagined — a top-secret stealth ship called the Sea Shadow that was built at the height of the Cold War using the technology developed for one of my favourite planes — the Blackbird SR-71.

Here’s to the urban explorers. Long may they thrive in secrecy.