Fieramilano is the world's third largest convention center, at 3.7 million square feet of enclosed space. It was designed by Massimiliano Fuksas and is a taut, elegant collection of eight huge halls, connected by a spine of glass and steel. It cost €755 million to build, almost a billion dollars.
I used to think that such things were white elephants, an artifact of an era before the internet showed us everything we needed. An urban planning disaster, taking people out of the city and dropping them in an ex-urban spaceship.
Then I visited it, as a guest of Machines Italia, and it was an eye-opener.