Location from harry-potter-chamber-of-secrets by
The hidden railway platform at King's Cross where the Hogwarts Express departs -- and where Dobby seals the barrier to prevent Harry and Ron from boarding, forcing them to fly the enchanted Ford Anglia to school.
This year the barrier refuses to let Harry and Ron through. They run at the brick wall and crash into solid stone, trolleys flying, owl cages clattering. Dobby sealed it with house-elf magic to prevent Harry from returning to Hogwarts. With the Hogwarts Express pulling away and no way to reach their parents, Harry and Ron make the spectacularly poor decision to fly the enchanted Ford Anglia to Scotland instead. They arrive, crash into the Whomping Willow, snap Ron's wand, lose the car to the Forbidden Forest, and nearly get expelled. It is the most Harry Potter solution to a problem imaginable.
A bustling platform wreathed in scarlet steam from the gleaming Hogwarts Express. Families in robes and Muggle clothes crowd the platform. The barrier from the Muggle side looks like a solid brick pillar between platforms nine and ten.
Also known as: Platform Nine and Three-Quarters, Platform 9 3/4, King's Cross, the platform