The gnome lad, Twelve, led the group down the hallway towards the giant brass vault door. He seemed a little surprised that he wasn't bombarded with questions but he quickly went into his tour guide speech anyway.
"Right. You're in the Klacken Exchange. We deliver magical solutions for a multiverse of problems. We exist in our own little pocket universe so time and space don't really operate the same here as it does wherever you come from. Take all the time you need here and when you are returned no time will have passed. Quite handy, that. No?"
As he led the his little tour past the ancient gnome still glaring at him the old man gave the party a quick once over and then gave his judgement.
"Vault 4."
With that delivered the old gnome shifted to stare at the bowl of water. Twelve gave an energetic nod and motioned for the group to follow him once again.
"Don't mind Number One. He just tries to run a tight ship after all. We try to hurry people through arrivals and processing to avoid any intersections...like the one you saw earlier. We are supposed to be neutral in all matters but that can sometimes mean our clients aren't pleased to see one another. That almost never happens...almost. My name is Josianamus Klackencogswheel, hence the name. Originally it was the Klackencogswheel Extraplanar Magical Exchange but none of our clients seemed to like that very much so it was eventually just shortened to the Klacken Exchange. I'm just the greeter, and cleaner, and messenger. I'll take you to your personal curator who will be able to explain things much more clearly than I can."
The gnome stopped about fifty feet away from the giant brass door. The door itself was covered with small engravings depicting various magical scenes. Wizards casting fireballs at dragons or reading ancient tomes or performing grand rituals. The engravings were so detailed that as the party walked forward the way the light and shadows hit the engraving caused them to appear to move. The fireballs would explore, pages would be turned, rituals circles would appear to glow. At first it looked magical but it quickly became apparent it was just expert craftsmanship and tricks of the light as the scenes just flipped back and forth over and over again.
"The key that you handed me is what we refer to as a guest pass. Our clients can get them issued to allow select guests access to our inventory. Sometimes it is just to do some shopping for the client but many times keys are given out as rewards for services conducted. Each key is single use however. Once your needs have been satisfied, within the limits of your client's tier of course."
Number Twelve, aka Josianamus, was standing next to a lever set into the marble floor. The young gnome began pulling and pushing the lever, flipping it through a complex series of positions. The ground began to rumble but instead of the giant vault door opening instead the whole wall began to rotate. Along nearly invisible seams the vault door and the wall behind it rotated clockwise so the giant brass door sank into the floor like a setting sun. As it did so on the other side of the wall opposite a new vault door came into view like a sunrise. This one was engraved with pictures of kings and rulers commanding armies and demanding loyalty from their subjects.
This door rotated up into position like the sun rising to midday but then didn't stop, it too continuing to rotate over and set, disappearing beneath the floor. A third vault door rose up and this was engraved with what looked to be heroes fighting terrible monsters or avoiding deadly traps. This time when the vault door was fully visible it locked into position. The gnome pulled the lever one more time and this time the giant vault door opened.
Through the door was what looked to be a giant warehouse filled with shelves.
Looking like library stacks but instead of books each shelf was full of boxes of varying shapes and sizes, each with a little card on the front labeling it. While the shelves themselves seem organized the overall layout is more akin to a maze and very little of the room is actually visible through the haphazard shelf layouts.
Standing on the other side of the vault are two more gnomes waiting patiently. One has a badge that says "#4" and the other has a badge that says "#8". Looking at them it would appear that the gnomes must all be related. Between #4, #8, and #12 it could easily be grandfather, father, and son.
Number Twelve runs forward, handing the key off to Number Four before heading back to man the lever, presumably to close the vault once the party had entered.