Alhorns are wooden instruments whose sound derives from the player's buzzing lips, as with brass instruments. They have no keys, valves, or other mechanisms to vary their length, as is common with most modern wind instruments. This limits the number of different pitches that can be played on an alphorn. This means that the full chromatic, major, minor, etc scales cannot be played. However natural harmonic series based on the pitch of the alhorn can be played. This makes the instrument similar to the bugle, meaning that Taps could be played on on alphorn. While this limits the types of melodies that can played on the instrument, it's long and rich history has produced a lage collection of alhorn music.

The Big Horn Alphorns instruments were made by Alfons Neumann of Alphornabu Neumann (in German) (English via Google Translate). They are comprised of three pieces, each approximately four feet long, for a total length of 12' 3".

You can read more about alphorns on Wikipedia.