A crow's nest is a structure in the upper part of the mainmast of a ship or structure, that is used as a lookout point.
This position ensured the best view of the approaching hazards, other ships or land. It was the best device for this purpose until the invention of radar.
In early ships it was simply a barrel or a basket lashed to the tallest mast. Later it became a specially designed platform with protective railing. 
Sometimes the term is used metaphorically in reference to topmost structures in buildings, towers, etc.
Since the crow's nest is a point far away from the ship's centre of mass, any small movement of the ship is amplified and could lead to severe seasickness, even in accustomed sailors. Therefore, being sent to the crow's nest was also considered a punishment. Spanish "carajo" curse is derived from punitive usage of crow's nest named as such in Spanish.
In hunting a crow's nest is a blind -like structure where a hunter or a pair of hunters commit themselves to stalking game. Crow's nest is not a normal type, purchaseable blind, but it is an improvised position, built by using locally discovered natural flora (tree branches, moss, snow (during winter) or sand (during summer) etc.) Crows nest works in most environments and provides a good look out point (hence the name) when built in elevated position (hillside, or top of the hill).In classic railroad trains, the box-like structure above the caboose, the cupola, was also called the crow's nest. It served for observation of the whole train when in motion. 

Decided to try a cache with a more challenging terrain type for all the adventurous geocachers out there. I had found the spot and felt compelled to place a cache here. This cache is quite precarious and should not be attempted under severe weather or if you aren't feeling confident about your climbing skills. It does have a nice view and is quiet compared to the surroundings. Please bring your own pen, since signing the logbook is a difficult  task as well. Have fun and happy caching! And for the record no "El Chanchos" were used in the placing of this cache.