Basilica of Saint Francis of Assisi, Kraków

Step inside and let your eyes adjust. The light here is not white. It comes through the glass in blues, violets, and deep golds, and it falls across the walls in soft, moving patches. Look up, and the walls themselves seem to grow. Painted stems climb the plaster. Flowers open above your head. The air is cool and smells faintly of candle wax and old stone. Footsteps on the floor echo, then fade. This is the Franciscan Basilica of Kraków.

Outside, the church stands on All Saints' Square, just a few minutes' walk from the Main Market Square. Trams rattle past on the street nearby. The building is made of dark red brick, heavy and plain, in the Gothic style of medieval Central Europe. From the outside, it looks serious, even severe. Nothing on that sober face prepares you for the colour inside. That contrast is the first surprise of this place.

The story begins with the Franciscan friars, the followers of Saint Francis of Assisi. Saint Francis was an Italian holy man who gave up his wealth to live in poverty and serve the poor. His followers spread across Europe, and they reached Kraków in the thirteenth century. Here they built one of the earliest brick churches in the city. Over the following centuries, the friars expanded it and added chapels and a cloister. The church grew with the city around it.

This was never a quiet side church. Kraków was the royal capital of Poland for centuries, and the Franciscan church sat close to the centre of power. According to a long-held tradition, the Lithuanian ruler Jogaila was baptised here in 1386, before his marriage to Queen Jadwiga made him King of Poland. Historians still discuss the details, so treat it as the city's own story. Either way, the church was woven into the life of the medieval kingdom.

Then came disaster. In 1850, a great fire swept through Kraków. It destroyed large parts of the city, and this church suffered badly. Much of the old interior was lost — altars, furnishings, decoration. For years afterwards, the building stood damaged and bare. The rebuilding was slow. And that long, slow recovery is the reason the interior you see today looks so different from any other medieval church in the city.

At the end of the nineteenth century, the friars invited a young local artist to decorate the walls. His name was Stanisław Wyspiański. Today Poles know him as a painter, a stained-glass designer, and one of the country's great playwrights. At the time, he was still making his name. He brought the spirit of the Young Poland movement — the Polish branch of Art Nouveau, a style built on flowing lines and forms taken from nature. This church became his canvas.

Look again at the walls around you. Wyspiański did not paint saints in heavy gold. He painted plants. Lilies, flowers of the field, twisting leaves and stems, all in soft, clear colours. Some of the patterns repeat across the vaults, and some change as you move along the nave. Many visitors walk in expecting dark medieval gloom and stop still. The effect is closer to standing in a garden than in a fortress of faith.

Now turn around and look high above the entrance. This is the second surprise, and many people miss it because they walk in facing the altar. The great window over the west door shows God the Father in the act of creation. Wyspiański called it, in Polish, "Let It Be." The figure is huge and almost wild, wrapped in swirling colour. On a bright afternoon, when the sun is low in the west, the glass glows with an intensity that feels almost alive.

The windows in the chancel, behind the main altar, are also by Wyspiański. They show figures linked to the Franciscan story and themes from the natural world, drawn in his strong, clear lines. Together with the painted walls, they make one complete design. Very few artists ever had the chance to shape a whole church interior like this. For Kraków, it remains one of the finest examples of Art Nouveau applied to a sacred space.

The basilica has a more recent connection too. Karol Wojtyła, who later became Pope John Paul the Second, lived and worked in Kraków for many years. He often came to this church to pray. Locals say he had a favourite place in the pews, and a small plaque now marks it. Across the street stands the Archbishop's Palace. From one of its windows, the Pope greeted crowds of young people during his visits home.

Before you leave, find your way into the cloister. This is the covered walkway around the friars' inner courtyard, and it is much quieter than the church. Some of the oldest Gothic walls survive here. Along the walls hangs a long series of portraits of the bishops of Kraków, painted over many centuries. Walking past them is a little like turning the pages of the city's history, one face at a time. Fragments of old wall painting also survive in places.

Remember that this is a working church. The friars still live here, and Mass is still celebrated every day. You may hear the organ during a service, or the low murmur of prayer from a side chapel. People come in from the street, kneel for a moment, and leave again. Move gently, speak softly, and avoid walking in front of anyone at prayer. The building belongs to them first, and to visitors second.

Take a final moment where you are standing. Notice how the colour on the walls has shifted, even in the few minutes you have been here, as the light outside changes. Notice the plain red brick when you step back out onto the square — so modest after the garden inside. As you walk towards the Market Square, you carry a small secret with you. Behind those heavy medieval walls, the flowers keep blooming.