The National Geographic photo contest has some great entries, including this one:
Hiking in pitch darkness within the dense forest undergrowth, one might encounter one of mother nature's awesome creations. A scene which many thought only belongs to the Sci-fi Movies. Filoboletus Manipularis is a fungus which naturally produces a faint eerie glow in the night by a natural process known as bioluminescence, shown in this 3-minute long exposure of these elusive little mushrooms.
Add some giant glow-in-the-dark mushrooms to you dungeon or sandbox!