Knock on the door, and you shall have an answer!
Open the heavy walls to set me free,
And blow a horn to call me into the sunlight,
And startled then what a strange thing you shall see!
Nuns, murderers, and drunkards, saints and sinners,
Lover and dancing girl and sage and clown
Will laugh upon you, and you will find me nowhere…
I am a room, a house, a street, a town.

Conrad Potter Aiken

http://www.poemhunter.com/poem/knock-on-the-door/