Vienna's historical and tourist center lies in the 1st District. Opposite the Palais Equitable (center left), St. Stephen's Cathedral is reflected in the Haas House (right), designed by Austrian architect Hans Hollein. Opened in 1990, the building, with its mirrored windows and curved, projecting façade, caused controversy. Is it a brutal eyesore or the arrival of modernism at long last?

Vienna has been ahead of its time before. This Jugendstil building from 1897/98 bears the inscription "To every age its art; to every art its freedom," the credo of the Vienna Secession, a group of artists led by the painter Gustav Klimt. They sought new, modern forms of expression in their works. An interesting architectural element is the leafwork dome which is nicknamed the "cabbage head."

Gustav Klimt (1862-1918) created a frieze, now in a special room in the basement, for an exhibition in 1902, taking Beethoven's 9th symphony as its theme. Over 34 meters, an interconnected series of frescoes depicts humanity's yearning for happiness.

The Beethoven frieze is considered a major highlight of Viennese art nouveau. It also began what is known as its creator Klimt’s Golden Phase. This “Choir of Angels,” and “Embracing Couple,” as well as his famous paintings “The Kiss,” “Judith,” and “Adele Bloch-Bauer” all belong to that period. The last-mentioned provided exciting material for the 2015 film “Woman in Gold” with Helen Mirren.

One of the world’s loveliest art nouveau churches was designed by the Viennese architect Otto Wagner (1841-1918). Built between 1904 and 1907, it’s considered the first modernist era church in Europe. His fellow artist Koloman Moser from the Vienna Secession designed the stained glass mosaic windows. When it was renovated in 2006, two kilograms of gold leaf were needed for the dome alone.

Altars, tabernacle, confessional box, a hygienically dripping holy water font, light fixtures and even the priests‘ vestments were made according to Otto Wagner’s designs. When the Church of St. Leopold opened it was criticized harshly by the Archduke Franz Ferdinand (1863-1914), who preferred imperial pomp and circumstance. The church can be viewed at weekends for an entrance fee.

Two pavilions on Karlsplatz show how beauty and practicality can be combined. They were set for demolition when the square's subway station was built, but after public outcry were renovated and reassembled two meters above their original level. They no longer provide direct access to the underground platforms. The western pavilion is now part of the Wien Museum; the eastern one is a café.

Apartment blocks were among the striking buildings Otto Wagner designed in Vienna during the late 19th and early 20th centuries. One is the Majolica House, at Linke Wienzeile 40. The architect, also a committed urban planner, had it covered completely with decorative floral tiles at his own expense. It was meant to be both beautiful and practical. The ceramic surfaces are easy to clean.

There was always a bridge at this location – first wooden, then walled. In 1904 the bridge over the street was rebuilt as an art nouveau structure, and it’s now historically listed. Views of its previous incarnations are engraved on its marble cladding. And by night the whole bridge seems to shine gold.