Within the same complex of buildings as the cathedral, and just adjacent to it, is the famous abbey library,or Stiftsbibliothek, one of the oldest libraries in Europe and classified by UNESCO as a World Heritage Site both for its stunning interior and for its huge collection of rare and unique medieval books and manuscripts. You enter the library beneath a sign reading, in Greek, psyches iatreion, or “Pharmacy of the Soul”. Ranged beside are dozens of pairs of oversized felt slippers – slip your shoed feet into a pair, to save the gorgeous inlaid wooden floor of the library from scuffing. The 28-by-10-metre room (April–Oct Mon–Sat 9am–noon & 1.30–5pm, Sun 10am–noon & 1.30–4pm; Dec–March Mon–Sat 9am–noon & 1.30–4pm; Fr.7; SMP) is acclaimed as Switzerland’s finest surviving example of a Baroque secular interior, and the first glimpse of it as you enter is dizzying. Designed by the same Peter Thumb who worked on the cathedral, the library dates from slightly later, so its orthodox Baroque architecture is overlaid with the opulent decoration of the Rococo period which then held sway. The four ceiling frescoes by Josef Wannenmacher depict with bold trompe l’oeil perspectives the early Christian theological councils of Nicaea, Constantinople, Ephesus and Chalcedon. Amongst the wealth of smaller frescoes set amongst the ceiling stucco, in the far southeast corner you’ll spot The Venerable Bede, a seventh-century English monk from Northumbria who wrote one of the first histories of England: he is shown as a scholar, with, beside him, a magic number square. This four-by-four sequence, where the numbers add up to 34 horizontally, vertically, diagonally and from the four corners, is thought to have been invented by Pythagoras in ancient Greece, but took on a new mystical power for early Christians who understood Christ to have died at 34 years of age.

The books are ranged on floor-to-ceiling shelves all around. You’re free to wander around and examine the spines – books were originally organized by subject, indicated by the cherubs at the head of capitals around the library, but are now arranged alphabetically. If you open the recessed panels between each bookcase, inside you’ll find registers of books in the nearby shelves with space to leave your name: the library still operates as an ordinary lending library and study centre, with some 140,000 volumes focused on the Middle Ages. Its list of cultural treasures is extraordinary – for a start, there are more Irish manuscripts in St Gallen than there are in Dublin, some fifteen handwritten examples from the seventh century and after, including a Latin manuscript of the Gospels dating from 750. Other works include an astronomical textbook written in 300 BC; copies made in the fifth century of works by Virgil, Horace and other classical authors; texts written by the Venerable Bede in his original Northumbrian language; the oldest book to have survived in German, dating from the eighth century; and a plan of St Gallen monastery drawn on parchment in the early ninth century to serve as a blueprint for construction of new buildings. Various of these and other treasures of the library’s upstairs manuscript room (no public access) are put on display in glass cases dotted around the main library area. An ancient Egyptian mummy in the library dates from 700 BC and was a gift to the mayor of St Gallen at the beginning of the nineteenth century; unsure of what to do with the thing, he plonked it in this corner, where it has sat incongruously ever since.