A Train Wreck, Toward the Light, and Someone's There are the first quests in Chapter 11, "Haunted", in Final Fantasy VII Remake, taking place in the Train Graveyard. Cloud Strife, Aerith Gainsborough, and Tifa Lockhart make their way to the Train Graveyard, and must then find a way to the Sector 7 Slums.
Walkthrough[]
From where the quest starts, a vending machine and a bench are available. The vending machine offers nothing new, but items can be restocked here. Equipping 
Ice Materia is useful here, to exploit the weakness of many enemies to 
Ice.
Head forward from the starting position and climb the ladder to the top of an abandoned train cart and proceed forward. Tifa will recommend the party move towards the light; take the ladder down and approach the light outside an open abandoned train cart; after some dialogue, head inside and go to the other end, where wererats appear, which can be defeated in simple attacks.
Mythril rod treasure.
After this defeating the wererats, there is a slight fork in the road. Heading right through another abandoned cart and further southeast leads to a treasure chest where the 
Mythril Rod can be picked up for Aerith; this weapon lends itself towards pure 
Magic Attack increases and provides Ray of Judgment, which can increase stagger damage bonus. Heading up a ladder to climb stacked carts and climbing down the other side will progress forward. A sound emanates from an empty warehouse, following which cripshays are fought; these enemies can be defeated with ice spells or abilities.
HP Up materia location.
Enter the empty warehouse and proceed through it, then run to an abandoned carriage on the lefthand side and arrive on the other side. After heading out onto the open, symbols appear on the ground, and then wererats and cripshays are fought. Once defeated, follow Tifa and Aerith up the ladder (the abandoned carriage on the southeast simply leads to a treasure with 1 gil) then drop down the other side and follow them further to an area where more cripshays are fought. Head north after this and head left to pick up the 
HP Up Materia, then head back right and further north to a ladder and climb it.
After climbing the ladder, ahead are piles of scrap stacked to form a straight path forward. Follow it and cross onto an abandoned carriage, leading to a cutscene. After this, head forward out of the carriage and join Aerith and Tifa in front of a gate. The gate opens, leading to the next mission, "Pass Through the Maintenance Facility".
Hard mode tips[]
The enemies here are more durable, but are not considerably harder. MP should not be expended here to conserve it for the boss later, but equipping 
Elemental Materia with ice materia on Cloud or Tifa is ideal. For most enemies, normal attacks with Deadly Dodge Materia on Cloud and Tifa are sufficient, along with Triple Slash from Cloud, Divekick from Tifa, or normal attacks from Aerith.