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In the Paddington Basin of the Grand Union Canal in London there a bridge that is usually curled up into an octagon but unfurls once a week for visitors to admire - and cross over.
This is the Heatherwick Studio's Rolling Bridge. It was commissioned in 2004 and needed to be a footbridge that would allow a crossing for local workers and residents but crucially could also move out of the way completely to allow boats to moor in the inlet.
We usually think of a bridge as a straight rigid structure but this one actually spends most of its life curled up next to the inlet looking nothing like a bridge.
Once a week, at around midday on Fridays, two members of staff from Paddington Waterside Partnership bring the controls to operate the bridge. Sometimes they have a little audience and sometimes they don't, but they always come.
It's a system of hydraulics that opens and closes the bridge which are fitted into the balustrade. It's a beautiful thing to watch as it appears so graceful for something that is so functional. The bridge can be stopped at any point of the 'curl' but generally there's no need and the operator will open stop it when fully open or fully closed.
When fully open, and across the inlet, people are allowed to walk over so do run round and try it. It's very stable for such a temporary structure. Once it's been used for a few minutes, and there are no people trying to cross, the second member of staff blocks the way for safety - remember you can still walk around the canal path - and the bridge curls back up.
Quite rightly, the Rolling Bridge has won awards but it can be frustratingly difficult to find so I've written detailed Rolling Bridge directions to help.
The Paddington Basin and the Rolling Bridge are mentioned in Tube London by Rebecca Sams along with lots more interesting London information.