Have your favourite pet blessed, visit an underground mine in the centre of Madrid, see the astounding liquefaction of the blood of Saint Pantaleon once a year, meet Spain’s only Catholic exorcist, find out how the king had his medicine made using alchemy, smell the apple odour that wafts once a year from the still-intact body of Mariana de Jesús who died in the 17th century, visit an underground art gallery, dine in a car park. . .  Madrid is overflowing with extraordinary and little-known places and curiosities. You just have to know where to look . . .  An essential guide for those who think they know Madrid well or for those looking to discover the hidden side of the city.