→ The Blue Chinese Salon — The room where Emperor Franz Joseph signed the 1914 declaration of war against Serbia. The Chinese hand-painted wallpaper was a diplomatic gift from the Qianlong Emperor — the same set decorates the room where the First World War began.

→ The Wagenburg — The carriage museum houses the imperial fleet, including the gold-leafed coronation coach used by Habsburg monarchs. The coach weighs over 4,000 kilograms and required eight horses to pull — too heavy for daily use, it was built purely for ceremonial display.

→ The Palm House — The iron-and-glass Palm House, completed in 1882, is one of the largest botanical conservatories in Europe. Its three climate zones required a bespoke heating system that burned 200 tonnes of coal per year.

→ The Imperial Treasury — The Schatzkammer holds the imperial crown of the Holy Roman Empire, the Austrian imperial crown, and the 2,680-carat Colombian emerald known as 'La Estrella del Sur.' The Burgundian Treasure includes a golden rose blessed by the Pope, one of only six ever made.

→ The Prunksaal — The State Hall of the Austrian National Library is a 77-metre-long Baroque hall containing 200,000 books from 1501 to 1850. The marble columns are not structural — they are painted wood, a Baroque illusion technique.

→ The Heroes' Square Gate — The Äußeres Burgtor, the outer castle gate, was built in 1824. The iron gate leaves are cast from captured Ottoman cannonballs melted down after the Napoleonic Wars — a literal recycling of enemy ammunition into imperial architecture.

→ The Catacombs — Beneath the cathedral lie the catacombs, where 11,000 plague victims were buried in mass graves during the 1713 epidemic. The tombs of the Habsburg dukes — containing the viscera of 78 Habsburgs — line the Ducal Crypt.

→ The Stone Pulpit — The carved stone pulpit from 1515 shows four Church Fathers: Augustine, Ambrose, Gregory, and Jerome. The lizard and toad carved beneath the stairs represent good and evil — a medieval visual shorthand the illiterate congregation could read instantly.

→ The Roof Walk — A 3.4-metre-wide maintenance walkway runs inside the roof structure, accessible by a 345-step staircase. The steel frame was installed in 1950 after the original wooden roof — the largest in Central Europe — burned in the war.

→ The Cascade Stairs — The water staircase between the Upper and Lower Belvedere uses a gravity-fed system: water flows from the upper pond through 21 cascades without a single pump. The pressure is maintained by the height differential alone.

→ The Sphinxes — The garden is guarded by 18 stone sphinxes, each with a different face. No two are identical — Prince Eugene commissioned them to represent the different peoples of his command: Turks, Hungarians, Slavs, and Germans.

→ The State Treaty Signing Table — The table where the 1955 Austrian State Treaty was signed is preserved in the Marble Hall. The inkwell used to sign the treaty was made from a meteorite — a symbol of Austria rising from the rubble of war.

→ The Dome Lift — A dedicated panoramic lift inside the church carries visitors to the top of the dome — one of the few Baroque churches in Europe with such an installation. From the cupola, you can examine the frescoes up close and see the brushwork of Johann Michael Rottmayr.

→ The Plague Memorial — The relief panels on the church doors show scenes from the 1713 plague — doctors in bird-beak masks, mass burials, and the imperial family praying. Charles VI is carved in the corner of every panel, watching.

→ The Rathausmann — The 3.5-metre iron figure holding a flag atop City Hall tower is the Rathausmann, Vienna's unofficial mascot. The flag is raised when the city council is in session and lowered when it is not.

→ The Museum Twins — The Kunsthistorisches Museum and the Naturhistorisches Museum face each other across Maria-Theresien-Platz. They were built simultaneously, are externally identical, and their domes were designed so that the distance between them equals exactly one-third the height of each dome — a deliberate optical ratio.

→ The Underground River — The Ringstrassen-Tram line runs above the Wienfluss, the river that was vaulted over in the 1890s as part of the Ringstrasse project. The river's concrete tunnel predates Vienna's U-Bahn system by 80 years.

→ The Children's Vault — A separate vault holds 12 children of Maria Theresa who died before the age of two. Their sarcophagi are miniature versions of the adult ones, with tiny crowns resting on pillows carved from solid stone.

→ The Heart and Viscus Separation — Three copper urns in separate alcoves hold the hearts of Emperor Ferdinand I, Archduke Franz Karl, and Archduke Maximilian. The viscera of the Habsburgs are preserved in St. Stephen's Cathedral, not here.

→ The Angel Sculptures — The four angels above the entrance, carved by Othmar Schimkowitz, are cast in aluminium — a material Wagner chose because it was modern and lightweight. Each angel represents a different cardinal virtue: Faith, Hope, Charity, and Justice.

→ The Separate Entrances — The church has three separate entrances — one for male patients, one for female patients, and one for staff. The patient entrances lead directly to segregated seating areas that were also separated by a low wall.

→ The Swimming Pool — The villa's indoor pool was one of the first in a European palace. The water was heated by a wood-fired boiler and filtered through layers of sand and charcoal — a 19th-century filtration system that kept the water clean without chlorine.

→ The Mirror Room — The dressing room is lined with mirrors arranged at angles that allowed Sisi to see herself from every direction simultaneously — she was notoriously self-conscious about her appearance and inspected her entire body daily.