Foxfire (or Glow-In-The-Dark Fungus)

Foxfire is a natural phenomenon sometimes visible at night in forests. It's caused by bioluminescent fungi in special conditions - usually on rotting bark. Foxfire is caused by a range of different species of fungi, though Armillaria mellea appears to be the most common source. The bluish-green glow is similar to glow-in-the-dark toys. Below are several example pictures taken from this photo gallery of foxfire in Japan: