In contrast to the grand marble of the entryway and the main hall, the passageways to the vaults are stone and dimly lit with flaming torches. They slope down to a track, upon which run little carts controlled by the goblins (DH26). These carts take visitors deep beneath the surface of the earth, through a “maze of twisting passages,” to the vaults. The carts only go one speed – fast – which makes Hagrid a little queasy and prevents its occupants from getting a good look at their surroundings (PS5), and seem to run on a vast, complex, interconnected series of tracks that allow them to move to and between any vaults (PS5, CS4).
The vaults themselves vary in size and security. The largest, most well protected vaults belong to the oldest wizarding families and lie deepest beneath the surface (DH25). Those vaults closer to the surface seem to be smaller and have fewer security precautions surrounding them – they use keys, for example, rather than requiring the touch of a goblin to gain access. We know of several vaults specifically:
The Weasleys’ vault, which is likely closer to the surface than Harry’s. When Harry visits, the vault contains only a small pile of Sickles and a single Galleon, and Mrs. Weasley cleans it out completely (CS4).
Harry’s vault, which requires a key for entry and seems to be of moderate depth – the cart travels for a while to get there, but it’s not as far down as vault 713, where the Philosopher’s Stone was held (PS5).
Vault 713, which stored only the Philosopher’s Stone when Harry visited with Hagrid. The vault was very deep and required a goblin to stroke the door with his finger in order to gain entry (PS5).
Vault 711, belonging to Sirius Black, from which he pays for Harry’s Firebolt. The fact that it is numbered so closely to 713 – coupled with the fact that the Blacks are indeed an old wizarding family – suggests that it too is a high-security vault (PA22). It contained a “reasonable amount of gold” (HBP3).
The Lestrange family vault, with even higher security than vault 713 – a dragon guards its entrance and rather than just a finger, a goblin must place his entire palm to the door to open it. The vault is filled with gold, armor, skins, and potions – and most importantly, Hufflepuff’s cup, which Harry steals (DH26).
Travers has a vault that requires a key, because he’s holding it when he runs into Hermione (DH26).
The rules around who is allowed to access vaults seem odd. We’ve seen wizards asked for identification (DH26) or a key (PS5) to be allowed access, yet both Molly (GF10) and Bill (HBP6) are able to get gold from Harry’s vault for him. Perhaps there is a charm forcing the wizard to give the gold to its rightful owner. However, even this wouldn’t explain how Sirius was able to send Crookshanks to order a Firebolt in Harry’s name, but take the gold from his own vault – despite being an escaped convict at the time (PA22).
It also seems that only blood relations can inherit a Gringotts vault; Dumbledore implies strongly that when Sirius died as the last of the Black family line, his vault was cleaned out and its contents added to Harry’s, rather than Harry inheriting the vault as well (HBP3).