The aether was thought to be the medium through which light propagates. For example, just as how sound needs a medium such as the air to propagate. It was once proposed to be an undetectable (by touch, smell or vision), extremely thin, elastic material that surrounded all matter and at the same time was permeable to all matter on Earth.
In 1887, A.A Michelson and E. W Morley conducted an experiment to show the existence of the aether by detecting its affect on the speed of light. It is now known as the Michelson - Morley experiment and has been repeated many times since.
Instead of boring you and explaining the details of the experiment, I'll provide an anology. Two identical swimmers start at the same point. One swims horizontally with the current (aether wind) and back against the current. The other swims vertically up and back across the current. Who came back first?
The result of the Michelson - Morley experiment was a "null result. This meant that the motion of the Earth through the aether wind could not be detected. The existence of the aether could not be proven.
This place isn't of much significance. I chose this area because at different seasons of the year, this alleyway can get extremely windy, hence a metaphor for the aether wind. It does get beautiful during sunrise and sunset as the light pierces through this gap and emits a bright orange glow, hence another aether wind reference. Can you prove the existence of the aether?
Advice
It is recommended to not geocache around the area on the weekends at the time 8:50 - 9:10 and 13:00 - 13:10. Lots of muggle parents about in their cars. Probably not a great idea to look for it at night as well, but it shouldn't be a problem.