Explore the walled city was a mission in Ratchet & Clank. After meeting the Commando at the city, Ratchet was ordered to infiltrate the compound on Batalia undetected, but was unable to make his way across a metal ventilation shaft without the proper gadget. He later on did find such a thing and returned to Batalia with the Magneboots in an attempt to stop the blarg destroyers.
The Magneboots will allow you to walk on the Magne-Strip, though simultaneously disables your ability to jump or use weapons other than the OmniWrench 8000. Be careful not to fall off, as the path is quite narrow, and you must steer clear of the scoutbots patrolling the area. Once inside, you must fight a lone blarg paratrooper, accompanied by several scoutbots and a blarg generator. Afterwards, head further inside to watch two cannonball tanks blow up part of the interior structure. Destroy these, as well as another swarm of scoutbots in a corner, then turn the bolt crank to open the rear gate. Travel to the island to finish this mission and transition directly into "Destroy the bombers".