A spiral has appeared over the past decade or so on the beach between Booterstown station and the Merrion Gates, southeast of Dublin. A sandbank (pictured) has gradually built up, driven by the action of the sea waves, and has assumed a form close to a logarithmic spiral.

We all know what a spiral looks like. Or do we? Ask your friends to describe one and they will probably trace out the form of a spiral staircase. But (...)