A plot twist might be that the goblins turn against Harry midway through his visit. They could be influenced by a dark wizard who has a grudge against Harry. This would completely change the course of his visit and force him to find a new way to achieve his goals in Gringotts. Another possibility is that the vault contains a magical item that has a mind of its own and tries to possess Harry when he touches it.
In fanfic, when Harry Potter goes to Gringotts, he might discover some long - lost secrets about his family's vault. There could be hidden spells or artifacts that were left there by his parents or ancestors.
In some fanfictions, Harry might meet a goblin with a special mission for him. This goblin could be an outcast among his kind and believes that Harry is the only one who can help. So, he takes Harry on a journey through the deepest parts of Gringotts, where Harry gets to see parts of the bank that no one else has ever seen. During this journey, Harry also meets other strange and interesting characters that are somehow connected to the goblin's mission.
He could encounter a new magical creature. The goblins at Gringotts are known to have various magical creatures guarding different vaults. Maybe Harry comes across a rare and friendly creature that helps him on his journey. For example, a small fire - breathing dragon that he befriends and it later aids him in a battle against Voldemort's forces.
Creatively, Gringotts can be a place of cultural exchange. Since it's a bank that serves both wizards and other magical creatures, it can be a place where different magical cultures interact. In a fanfic, Harry could witness a meeting between a goblin banker and a centaur who is trying to deposit some rare magical herbs as collateral for a loan. This could lead to all sorts of interesting storylines about cultural differences, misunderstandings and cooperation within the magical world.
One possible fanfic could be about Harry Potter starting his apprenticeship at Gringotts and uncovering secrets about the bank's vaults. He might learn about the magical security systems and the history of some of the most powerful magical artifacts stored there.
In certain fanfiction stories, when Harry goes to Gringotts, he could be on a quest to retrieve a powerful magical artifact. Along the way, he may meet new characters, either friendly or hostile. He might have to fight his way through various security measures, which could include things like enchanted doors and traps. And his visit to Gringotts could be a turning point in the story, setting off a chain of events that will change his life and the wizarding world around him.
Maybe Harry has to compete in some magical challenges set by Gringotts to retrieve a powerful magical item. For example, he might face enchanted vault guardians.
In the 'Harry and Bill visits Gringotts fanfic', they might encounter various magical creatures and security measures. Maybe they are on a quest to retrieve a valuable item from a vault. They could face challenges like tricky puzzles or dangerous traps along the way.