The Eiffel Tower has a new rival, five centuries old.

For the first time since it was built in the early 1500s, the Tour Saint Jacques,  a mysterious stand-alone Gothic tower in the geometric centre of Paris, is opening to the public this summer.

The 170ft-high tower, long surrounded by myths and legends, has literary connections ranging from Alexandre Dumas to Marcel Proust. It was used by the writer and scientist Blaise Pascal to experiment with atmospheric pressure  and weights a century before Isaac Newton developed his theory of gravity....