Keret House in Warsaw

You're standing where Chłodna Street meets Żelazna Street in Warsaw, at Keret House. Look carefully, because it's easy to miss. Between a pre-war house and an apartment block there's a narrow gap, and tucked into it is a tiny house. It's often called the narrowest house in the world. At its thinnest it's ninety-two centimetres wide, and at its widest about a metre and a half.