I think the CST train station building in Mumbai, the Birds Nest in Beijing, and the Burj Dubai Hotel ( because I have a thing for sailboats) could be contenders! I haven’t personally seen the Birds Nest building.
And WHO thinks arches are beautiful? They have zero utilitarian value, and just define space.. basically!
Edit: It's a reference
Basically every cathedral in Europe that's been maintained.
The Nemours Estate, the South Carolina State House, and the Old Parkland are also contenders.
Sacre Coeur, Paris
St. Basils Cathedral, Moscow
Winter Palace, St. Petersburg
Palace of Versailles, Paris
Palace of Westminster, aka Houses of Parliament, London
Neuschwanstein Castle, Bavaria, Germany
Cologne Cathedral, Germany