Between about 18th and 30th April, if you are in central London, it may be worth visiting Tower Bridge for an unusual sight.
The details are in the Port of London Authority Notice (PDF file). Basically work is to be done on a couple of arches of Tower Bridge by men on ropes dangling from the the arches which will on some days be closed to navigation. At other times the arches may still be open to navigation but with reduced headroom when the byelaw requires that the Bridge Master hang a bale of straw "large enough to be conspicuous" from the centre of the arch by day (and a white light by night).
And of course one must not forget that Tower Bridge is officially registered as a ship.
Surely only in this country do we have such arcane, and legally enacted, requirements!
Hat-tip: Ian Visits