Klementinum

Most visitors walk straight past the Klementinum on their way to Charles Bridge without realising that behind its long, plain facade lies one of the most beautiful rooms in Central Europe. This vast complex, the second-largest building in Prague after the castle, grew from the seventeenth century as the Jesuit college of the city, and today it houses the Czech National Library. Its showpiece is the Baroque Library Hall, completed in the early eighteenth century: a long, barrel-vaulted gallery lined with carved wooden shelves of theological books, its ceiling painted with frescoes and its floor set with a row of astronomical and geographical globes. It is a genuinely breathtaking sight, the room people mean when they call Prague a fairy-tale city. The visit is a guided tour of about 45 minutes, run in English and Czech, and it is the only way in. It takes in three spaces. The library hall comes first, and here is the one thing to know in advance: you view it from the doorway, behind a rope, rather than walking through it, because the hall and its books are protected. Then comes the Meridian Hall, where a thin line and a small hole in the shutter let the sun mark true noon, a signal once relayed by flag to the city. Finally you climb the Astronomical Tower, 68 metres high, by 172 steep, narrow steps to a balcony at about 52 metres, with a statue of Atlas on the roof above you and a close-up view of the Old Town towers, Charles Bridge and the castle across the river. Tours are capped at 25 people and sell out at busy times, so book a slot rather than turning up. It is the single most rewarding hour you can spend indoors in the Old Town.

The history is the story of Prague itself. The Jesuits arrived in the sixteenth century and built their college here as the spearhead of the Counter-Reformation in a largely Protestant city, demolishing whole streets to make space. After the order was dissolved in the 1770s, the Klementinum passed to the university and became the home of the national library, and the tower became an observatory: continuous weather records have been kept here since the late eighteenth century, one of the longest such series in the world. Behind the facade there are courtyards, chapels and the Mirror Chapel, which is used for concerts; the guided route, however, concentrates on the library, the Meridian Hall and the tower, which are the parts worth your time.

Working the visit: the official visitor page lists the basic adult ticket at about 380 CZK, with reduced, youth and family prices, free entry for small children and a half-price discount on the first two tours of the morning. From November the day starts earlier and runs later, so there is a wide choice of slots; the first tour of the day is cheaper and quieter. The tower climb is the only demanding part. The steps are steep, spiral and wooden near the top, there is no lift and the building has no step-free route, so it does not suit anyone with limited mobility, a fear of heights or a pushchair. Photography rules can be strict in the library hall, and guides will tell you what is allowed. Wear shoes with grip and leave large bags at your hotel.

Fitting it in: the Klementinum entrance is on the Old Town side of Charles Bridge, between the bridge and Old Town Square, so it slots naturally into a first-day walk along the Royal Route. Pair it with the Old Town Bridge Tower for a second rooftop view, or with the Old Town Hall and Astronomical Clock five minutes away. In winter, a late-afternoon tour gives you the tower view at dusk with the city lights coming on. The Tiqets link opens the Klementinum venue page, where you can compare tour slots and passes; the Prague Visitor Pass has included this tour in the past, so check before buying a separate ticket if you already hold one.