Magic Item: Coach of Holding

I fully admit that I have no real sense of scale when it comes to providing my players with magic items. I do know that I want them to seem, where possible, unique and strange, and that a good way to keep items balanced is to give them limited uses, or to make their size completely impractical. This one uses the latter:

The Coach of Holding

The coach is a fairly new legendary artifact, with fresh paint and bronze fixings that show just a hint of wear and tear. From the outside, it appears to be a gaudily painted stagecoach, with tall wheels and enough apparent room for six people. Its strangest outward feature is that it has no windows and only one small door in the rear, three foot square.

Upon entering the coach, one finds nothing but a random scattering of some of, but not all of, whatever the coach contains. The coach's magic only works when the door is closed and all light sources are extinguished.

When lamps are re-lit, those inside find themselves in a pitch-black, seemingly infinite tin-floored plane. Everything ever placed inside is scattered around in every direction, some father away than others. Nobody has ever found the walls or ceiling in this place, though many have tried, and it is said some of them still wander in the coach's directionless otherspace. Sometimes enterprising nobles have funded expeditions deep into the coach's interior, ransacking whatever is found there. It is not known for certain that all of these groups have returned.

The coach can be moved when people are in it, though there is no mundane way of telling. Despite the fact that nobody within the coach has ever felt it move - even when, on one occasion, an angry and terrified mob flipped it completely after an accused witch took shelter inside - there is some evidence that the external forces it experiences change the distribution of objects within. After long and bumpy journeys, or transportation by sea, items stored inside have been found strewn about, but months or years in stationary storage will leave everything stacked as neatly as it was before. 

Except for, perhaps, a few small baubles, or a sack of grain, which disappear without a trace.

Game Terms

The coach is eight feet long, five feet tall (nearly nine, with wheels), top-heavy and prone to tipping. It always requires to draft horses to pull. It detects strongly of magic - anyone detecting magic within two miles will sense the coach, like a distant flame. There is no known limit to its internal size or capacity - anyone searching for an item inside the coach will take 1d6 turns per day of travel the cart has been used for. If the cart hasn't moved at all (even a minor earthquake, or a group of people shaking it counts as a "day of travel") the item is right where it was left, and it takes only 1 turn.

Searching the cart tends to turn up a lot of ancient detritus. Every time someone enters the cart, roll 1d20, adding the number of turns spent, and subtracting 20. The total is the number of random items found, each 1d20 (exploding on a 20) years old. Write your own random item list, or use this 1d100 table.

As for the coach's other mysteries? Those are yet to be discovered...