Everyone goes somewhere when they sleep. Dreamland is the most common name, but some just think it's your unconscious figuring itself out or filing away memories. But then there are those who knows what it really is. A whole other world where your true self, the self unbound by your physical body, is able to go. In this world, if you can focus yourself enough to consciously travel it, is a shop. A funny little shop keeper knows the ones who are awake in this world and those who travel within it asleep. The sleeping ones can't get in. The ones who are awake are welcome with a smile, the tinkle of a bell, and ask What dream will you trade me for my items today?
If you've ever awakened in the morning to find an unusual object on your nightstand you swore you'd never seen before, but somehow know it's your's? It means that you were able to wake up in that world and travel to the shop.