Crinkle-crankle - great word isn't it? And here's a picture of one:
A crinkle-crankle is basically a wobbly wall - one that undulates along its length. They were originally designed to grow fruit trees on. The waves increase the length of wall that faces the right way to have maximum sunlight. The bends also make the wall stronger so they don't need buttressing.
They were common features of 18th century gardens but fell out of fashion and are rarely seen on modern developments. So I was delighted to find this one along the back of a Tesco car park in Beeston, Nottinghamshire.