Link finds a way back to the Twilight Realm years after the end of Zelda: Twilight Princess. Link persona highly recommended.
Midna shattered the mirror which connected the light realm and the twilight realm, fearing that the two races could never coexist in peace. She did so in spite of her feelings. However, Midna's duties as a newly appointed monarch gave precedence over all else. She had to shatter the mirror and separate the realms.
Link was desolated. Midna's separation was unexpected and left a big hole in his heart. He tried to settle down back to his old life after being a hero, but when the hour of twilight came his mind always wandered back to Midna. Her presence, and thoughts of what could have been between them. They never had the chance of declaring the feelings for each other.
So, Link set out into the world, searching every corner of Hyrule and beyond for a non discovered way of going to the Twilight Realm. He spent years searching, encountering different races of people and fighting unexpected and terrible evils. After over three years he found an amulet which can create a portal that can transport someone anywhere they wish. He braced himself, wishing to see Midna, and crossed over - finally emerging to the Twilight Realm. The eternal sepulcre in which the realm always found itself was just as he remembered.
Now, he had to find Midna. The castle is a logical choice, with its super tall towers visible from afar.
Link was a hero to these people, years before. He wondered if he'd be remembered, and how Midna would react seeing him.
He put the hood over his head, covering his face and the sword on his back. He clutched the amulet which created the portal in his hand, and walked forward.