A sprawling floating metropolis located on Bespin, Cloud City is where Boba Fett and Darth Vader tracked down Han Solo, Chewbacca, Princess Leia and C-3PO after they had escaped off of Hoth
Cloud City is also where Luke Skywalker learned the secret that Darth Vader was his father.
Boba first came to Cloud City many years before after he was picked up by some Clone Soldiers on Raxxus Prime. It was on the Acclamator-class troopship, the Candaserri, that Boba, calling himself Teff, met the young Jedi Padawan Ulu Ulix.
StarWars.com Databank entry: [Cloud City]