If there's a more unassuming museum in zone 1 than the Kirkaldy Testing Museum, we'd like to know about it. Hidden in plain sight on Southwark Street, in a building opened in 1874 specifically to house it, is a unique piece of industrial heritage — David Kirkaldy's testing machine, a kind of Victorian independent lab for checking whether building materials were strong enough to handle the job.
Links for the Hammersmith Bridge were all placed into the impressively sized machine and had huge amounts of stress placed on them. Those that passed went into the bridge; those that broke were (obviously) thrown away. You're welcome, Hammersmith. We didn't get to see the machine in action, but it gets fired up on the first Sunday of each month.
There's a lot more to see in the museum as well: get hands on with lots of other, smaller, machines (we discovered plastic packing tape can take the weight of more than a grown man before it breaks!), see roundels from the original Blackfriars railway bridge and just explore the building, including a secret passageway where you can see people walking in Southwark Street above your head.
The museum will also be open during the MERGE festival when it'll play host to a site-specific interactive audio-visual artwork. The testing machine won't be working, but you'll get to poke around the building for free.
The Kirkaldy Testing Museum is at 99 Southwark Street. Open days are the first Sunday of every month; entry costs £5/£4. If you'd like to get involved with helping to run the museum, get in touch with the trustees via the website or Twitter.