Magical gate to another world

I came up with a theory today: the shop contains a magical portal into another world.

So often people come into the shop and we go through the usual, "hello, how are you today?" "oh fine thanks, I'm just looking" "okay well let me know if I can help you with anything." I see them go to the back of the store, look at the shelf unit in the kitchen and after that point I never see them again, not even leaving the store. I've even gone in search of people upstairs and in the bathroom because I never see them leave and I wonder what has happened to them. Surely I can't be so oblivious as to miss entirely someone's exit from the back of the store to the front door.

I am now quite sure that the door way between the front of the shop and the back room can transport those who know how to use it into a magical world. Otherwise, how else do these people disappear? I never hear the back door open or close, I never see them leave via the front door, I never find them wandering around upstairs or nor even crouched in the bathroom.

Now I want to know, what magical fairyland are these people transporting into? And can I come?