Podroth! What, the name doesn't mean anything to you? Then please, allow me to introduce you!
Podroth is a world like our own, a three-dimensional space where people live, laugh, and labour, where there are stars in the heavens and sand on the seashore, and where money is made by buying and selling goods in huge cities. In fact, the name Podroth actually applies to the dominant trade city, but since this is the part of the world of most interest to travellers, the whole world is referred to as Podroth.
In Podroth, magic is a well-known phenomenon. Not everyone casts spells by any means, but everyone knows that spells can be cast. Young boys and girls will yearn to become mages, just as they yearn to become firemen or any other glorious career, but in the end, it's just another calling like any other. But superior to all mages are the "dimension-walkers" or "walkers", those fabled mages who have the ability to traverse the great emptiness of the "sixes".
The universe has actually more than the three dimensions we know. Anyone can move in three dimensions, but with the aid of powerful magic, one can step out across six - and the entire world of Terra or Podroth becomes just a bright point of light in the vastness of space. The "sixes" are not empty in the way that a room can be empty; they are not even empty as is our knowledge of outer space. The emptiness here is utter and complete - not a fleck of dust, not a mote of air, no light, nothing. Stepping out requires magical power sufficient to overcome the gravity of an entire world, and once you are moving, you must keep moving until you find another world in the blackness. A dimension-walk is a very serious undertaking, and cannot be done safely while distracted; but as a means of escape, nothing beats leaving the world altogether.
Walkers visit Podroth only rarely, and there are none known to be native to it. A walker's visit is therefore a momentous occasion, one of either great joy or great fear, depending on the walker's outlook toward the local peoples. For the laws of the land cannot restrain a dimension-walker - there is no punishment that can be enforced on one who cannot be tracked down. There is an entire organization devoted to following walkers' movements and noting when they visit; these "walk-trackers" do their utmost to ensure that any visiting walker is made welcome and is treated with respect, in the hopes of maintaining good diplomatic relations.
Between visits, and for most people even during visits, life goes on without any reference to the walkers. People live, work, conduct business, often without any reference to magic, much less dimensional travel. And that's as it should be...