Igreja do Carmo & Igreja dos Carmelitas

Two churches pressed so close together they share a wall — and the reason is one of the most absurd pieces of Portuguese bureaucracy in history. Canon law prohibited two churches from sharing a wall, so when the Carmo Church was built beside the Carmelite Church in the 18th century, a house exactly one metre wide was constructed between them to satisfy the rule. The narrowest house in Porto stands between two of its grandest churches, and it was occupied until the 1980s.

The Carmo Church's side wall is the real attraction — a vast azulejo panel installed in 1912 depicting the founding of the Carmelite Order on Mount Carmel. It's one of the largest tile panels in Porto, covering the entire lateral façade in blue and white, and the scale is staggering when you round the corner and see it for the first time. The tiles were painted by Silvestro Silvestri and are in remarkable condition for being exposed to Atlantic weather for over a century.

The interior of the Carmo is Baroque and gilded — Porto's default setting for church decoration — while the adjacent Carmelite Church (Igreja dos Carmelitas) is slightly earlier and slightly more restrained. The one-metre house between them is not open to the public, but you can see its tiny door from the side street, and imagining a family living in a space narrower than a hallway while flanked by two enormous churches is one of Porto's more entertaining mental exercises.