Solution message:
Code certitude : PALAISROYAL
Solving that second puzzle gives:
Code certitude : SEINEORSAY
Solving that third puzzle gives:
Code certitude : SALVADORDALI
Solving that fourth puzzle gives:
Code certitude : GALERIEDELEVOLUTION
Solving that fifth puzzle gives:
Code certitude : ANTENNERADIO
Soling that sixth puzzle, which is ludicrously easy compared to all the rest (only 36 pieces rather than 540!) gives:
Code certitude : CHOCOLATINE
Joining all those codewords by semicolons and entering them into https://www.certitudes.org/certitude?wp=GCA5JNG gives:
N 48 51.166 E 002 18.884
Phew!