'The Cathedral of the Sea' Walking Book Tour in Barcelona. Bring ‘The Cathedral of the Sea’ — Ildefonso Falcones’ stirring debut novel — off of the pages and into real life with this guided walking tour of Barcelona. Explore the Gothic Quarter and the trendy El Born district with a knowledgeable guide, and visit the Church of Santa Maria del Mar, the construction of which provides the backstory for Falcones’ thriller, as well as other locations featured in the book. Book and Save 10%! 'The Cathedral of the Sea' Walking Book Tour in Barcelona.