Shipton's Arch

China Chas has added a photo to the pool:

Underneath Shipton's Arch, the tallest natural rock arch in the world. The arch is believed to be approximately 400m tall, with a span of around 60m.

It's very hard to get a good idea of the scale of the thing as you cannot get directly underneath: just in front of where I was standing, the mountain falls away in a sheer drop down to a canyon hundreds of feet below, a dangerous place due to constant rockfalls from the weak sandstone.