Beyond the Dead End, Dangers in the Debris, Working Together Again, and Saying Goodbye are quests in Chapter 9, "The Town That Never Sleeps", in Final Fantasy VII Remake, taking place in the Collapsed Expressway. While Cloud Strife and Aerith Gainsborough travel through Sector 6 on their way to escort Cloud back to Sector 7, they hit a dead end.
A vending machine and a bench can be found; the "Cosmo Canyon" track can be purchased for 50 gil, along with many previously available equipment. Use the bench to heal HP/MP and proceed to the next quest.
Head back from the vending machine to look for a ladder leading down to a lower level. Lesser drakes are fought here, best defeated with ranged attacks from Aerith and spells. Take the ladder down and head through the sewers on the lower level then open a door. Before opening it, equip the Fire Materia on Cloud or Aerith.
After opening the door and a short cutscene, the bandits Beck, Burke, and Butch are fought. They can simply be defeated with normal abilities, though Fire and Fira can also deal with them swiftly. Their only threatening attack is their ability to stun Cloud or Aerith if they are trapped in their electric mines; avoid this, and the fight should be simple.
Once the bandits are defeated, proceed forward, using the small gap, and proceed through a linear path then take a ladder up. On the other side, bandits appear along with a Sweeper Prototype. Defeat the bandits first to remove the threat of being stunned, and focus on the sweeper's right and left arms to stagger it, then lay into it with normal attacks.
After this, use the console to control the arms located here, which can be switched between using . Use the closer arm to move a container to a slot further right (marked by yellow), then use the further arm to move the container further left and stack it on top of the previous container. Next, switch back to the closer arm and move the stacked container to a slot further right, in front of a tunnel, and move the arm back to the bottom end to give Aerith a lift onto the container near the tunnel, allowing her to pick up the Magnify Materia. Pick the container on the right back up and stack it back onto the left container, drop Aerith onto it with the closer arm, then switch to the further arm and give her a lift to the spot on the right. Run down and climb the ladder she dropped for a short cutscene.
After this, run to the right and use a ladder upwards. A few more bandits are fought ahead, which can be dispatched with spells. Run forward through the gap and hold to give Aerith a thumbs up, then head forward to the Evergreen Park. After the cutscene, follow Aerith and approach her for another cutscene; once it ends, talk to her and agree to go to the Sector 7 slums, at which point a cutscene commences. This leads into "Chasing Tifa".
Hard mode tips
As with before, equipping Cloud with the Provoke Materia can be helpful to keep the less durable Aerith alive. Aerith can stay at a distance casting spells paired with either MP Absorption Materia or HP Absorption Materia, and using Soul Drain as Aerith is worthwhile to deal damage and restore MP. Fire materia is still the most useful damaging materia here, though Lightning Materia should also be used. Another good strategy is to give Aerith First Strike Materia, allowing her to open with a spell (or an Arcane Ward followed by a spell).