I guess I'm partial to the Parthenon. I was amazed at the workmanship and hard labor it must have took to build such a beautiful building. Super architecture! What it must have looked like in ancient times is mind boggling.
I quite like "Il Vittoriano" in Rome's Piazza Venezia.
Even though it's kind of controversial because it's glaringly white and an entire neighborhood that had been around since the Middle Ages was levelled in order to build it.
It was originally built as a symbol of a unified Italy.