Once I was staying in a small coastal cottage on a headland at Cornwall, and - on an otherwise calm and peaceful night - I was awoken by the screams of excited girls, as if standing next to a Ferris Wheel at a fairground.
The screams became louder as the beam of the nearby lighthouse swept past and through the window of my little room, casting a fleeting light on the ceiling which - after three nights at the cottage, I was well used to - then receded into the distance with the light. I got up and went to the window to investigate.
Out to sea, Mermaids were leaping from the water like dolphins, catching the sweeping beam of light, clinging on with slippery, wet hands and being flashed past the cottage and over the jagged rocks of the cliffs before letting go with whoops of delight and falling the 200 feet back into the water to swim around and catch the beam again.
It was late, and I now regret shouting out of the window to tell them to shut up and let me sleep. In the morning, of course, they were gone and they did not return the following night.