There is a series of valleys in Wales, United Kingdom named The Mach Loop and after seeing this video by YouTube user Wonkabar007, we now know why. The valleys, located 8 miles east of Barmouth, are used as a low-level training ground for the both the English Royal Air Force and the United States Air Force. According to World War Wings, the location is used to train fighter pilots how to fly in mountainous regions while avoiding radar detection.
The Mach Loop seems to open to anyone, and photographers, aviation enthusiats and curious bystanders stand on the rock croppings waiting for the close flybys, which we can only imagine will make your adrenaline jump. The government of the United Kingdom provides a online schedule of the training sessions in the Mach Loop which will help you plan your close encounter.
Here is another great video from the Mach Loop from Jesper Rådegård.
[Via World War Wings]