Congratulations to Swayambhunath, but I still like Etemenanki and Château Frontenac more
However, here are my suggestions:
Castel del Monte (Italy)
Castel Sant'Angelo/Mausoleum of Hadrian (Rome, Italy)
Galata Tower (Istanbul, Turkey)
Grand Bazaar (Istanbul, Turkey)
Ještěd Tower (the Czech Republic)
Lotus Temple (Delhi, India)
Národní Divadlo/National Theatre (Prague, the Czech Republic)
Oost-Indisch Huis (Amsterdam, the Netherlands)
Pilgrimage Church of Saint John of Nepomuk (the Czech Republic)
Pont du Gard (France)
Prague Astronomical Clock (Prague, the Czech Republic)
Sagrada Família (Barcelona, Spain)
Ziggurat of Ur (Iraq)