Frustrated Internal Reflection

If we have a large piece of material like glass and light (or any sort of electromagnetic radiation, really) is traveling through it, if the beam is close to perpendicular to the surface of the material, it refracts off of the surface on exiting. This is the phenomenon that causes the distortion you see of a straw inside a glass of water.
If, on the other hand, the light is far enough from perpendicular to the surface, it undergoes what's called total internal reflection, and none of the light gets out of the material. It's a well-known phenomenon, and among other things, it's what makes optical fibers work so nicely. But that's not the interesting physics, at least not for now. Rather, it turns out there's a way to frustrate the internal reflection by a quantum effect.
Basically the way this works is that the electromagnetic waves propagating through the material don't end exactly at the surface of the material. This is a result of how particles behave when they encounter a barrier - it's a quantum effect. Instead, there is a non-negligible amount of this radiation within a few wavelengths of the surface outside. If you bring some of the same material close enough to the surface, the electromagnetic wave residing there see it and can start propagating through the other material. It's amazing, if you think about it - normally, no light escapes the first block of material. But if you have some more glass nearby, the light can tunnel through the gap and continue propagating!
Unfortunately this is a little tricky to observe with glass and visible light, as the wavelength of visible light is so small that the second hunk of glass has to practically be in contact with the first, which makes the tunneling somewhat difficult to observe. But if you instead use microwaves instead of visible light and polyethylene instead of glass, the gap can be as large as a couple of centimeters. Quantum tunneling on a macroscopic scale - awesome, eh?