A night cache is a variation of the Mystery Cache type that can only be completed at night.
A night cache could be looked at as a variation on a traditional cache. In it's basic form it is set up just like a traditional. It is a result of the added aspect of finding it only at night that it is commonly listed as a mystery cache.
A night cache is built by placing a cache container at a desired location. Usually, that location is a wooded trail though successful versions have been placed in more open areas. Once the cache container is placed, the owner then uses reflective tacks to mark the trail leading to the cache container. When doing this, it is important that a geocacher can see the reflective tacks while approaching the cache container, not the other way around. Many cache owners will put single tacks on the trail, and a set of multiple tacks side by side at the location of the final cache container. The owner then marks the location of the start of the trail and lists those coordinates when creating the cache page.
To find a night cache, a geocacher must go to the listed coordinates with a flashlight. Standing at the starting coordinates, the geocacher will shine the flashlight around until they see the reflective tack light up. They then move to the spot where the reflective tack is located and repeat the procedure. This is done over and over again until you reach the final cache location and find the container.
There are variations to this method. One involves hiding a container next to each tack (or using larger reflective tape) and putting the coordinates to the next stage's starting point inside. Another variation involves placing puzzles to solve at each stage.
Night caches may also use invisible ink, lights and glow in the dark materials.
Reflective tacks are commonly used by hunters to mark trails to their blinds. You can usually find them in hunting stores/departments. Reflective tacks typically come in a variety of colors, including white, orange, and stealth. Stealth blends into trees easier in the daytime, but sometimes don't shine as bright as the white or orange ones. Fire Tacks is a popular brand of this product, known for their highly reflective designs.