You leave Zürich none the wiser, although you feel you might have seem something important. Perhaps Madrid will furnish you with a Spanish clue?
Unsure where to start, it’s not long before you become entranced by the pristine tiled floor of Catedral de la Almudena. Naturally it reminds you of a puzzle:
Connect the two HOPR dots with an orange path that’s 1 square wide at all points. The path travels horizontally and vertically, but never doubles back to touch itself, and there is never a 2x2 orange square. (The path can double back to touch itself diagonally.)
Any square which is not on the orange path should be coloured blue. Each blue square is part of a region of EXACTLY five blue cells. (One is already given, other shapes can vary or be the same.) These regions can touch diagonally, but not horizontally or vertically - or they’d be larger than 5 squares!
The answer is the order of colours down the northwest to southeast diagonal. (So it starts OBB…)
(Many thanks to NB for lending this neat puzzle idea.)