Metropolis

Metropolis is the capital city of Planet Kerwan, and one of the biggest cities in the Solana Galaxy with over 3 trillion inhabitants. Al's Roboshack is also located in this city, along with Captain Qwark's fitness course. In the city you can see all kinds of things like futuristic skyscrapers, flying cars, Flying Trains (or Grav-Trains), skywalks, Blimps, and all kinds of neat features throughout this massive city.

In Ratchet & Clank, the duo arrive here in search of Captain Qwark. It is here that they first meet Big Al and Helga, Qwark's fitness trainer. Eventually, they take a Grav-Train to catch an Infobot.

In Ratchet & Clank: Up Your Arsenal, Dr. Nefarious unleashed his Biobliterator upon the city, turning many of the citizens into cyborgs. It was also here that Ratchet faced Klunk on two grav-trains one of them with clank inside a cage. It is also important to note that Metropolis is not the capital city of the galaxy (which is actually Capital City, on planet Marcadia).

In Ratchet: Deadlocked, Sasha becomes the Mayor of Metropolis.

In Ratchet and Clank Future: Tools of Destruction, the city was attacked by Tachyon and his army of Drophyds when Qwark informs the duo that he is under attack at the planetary defense center. When Ratchet and Clank got there their was no sign of him only to be confronted by Emperor Percival Tachyon's minions that tried to exterminate Ratchet who escaped with Clank on a grind rail dodging grav-trains, gunships, and Tachyon's imperial warship who confronted them at the end, with Tachyon coming out of the warship he said behold the last Lombax of the Universe. After the attack, Metropolis went through a rebuilding stage and the citizens had to watch Big Al's Bot Wars.

Vid-Comic
Metropolis is also a mission in the vid-comic missions that appear in Up Your Arsenal. At the end of the level, Captain Qwark duels with Dr. Nefarious himself.

Trivia

 * Insomniac Games decided to put Metropolis on planet Caldera first but later on it changed to Kerwan.