TheViewShed is a community driven visual directory of line-of-sight views from around the world.
The 'source' must be from the ground on Earth (including on hills and mountains) or from a man-made structure attached to the ground.
The 'destination' can be just about anything one can see from the source (that is also ground or attached to the ground on Earth).
This means that photos or view-claims cannot be from planes, drones, hot air balloons, rockets or space stations.
This also means being able to see Mars from your house, while cool, is not included.
We've set the limit to anything over 10 kilometres (~6.2 miles).