Written for solo guitar by Cuban composer Leo Brouwer, this piece is usually the example of contemporary guitar composition both in terms of actual exploring the instrument's possibilities in producing sound, and composition techniques.
Written in 1971, it makes use of the various possibilities the guitar has in extended technique and also different composition techniques, and with these elements it forms a structure based both on the nature of the sounds produced but also on composition techniques as contrast.
Guitarists probably know this piece and hopefully play it, but someone who isn't well versed in the instrument may not know of it.
As far as composition techniques go, this piece uses indeterminacy in establishing which notes are to be played during the various sections where this technique is used. This is a middle between aleatory techniques and certainty of tone, which translates to the musician playing notes "around" a specific region in the guitar's register.
Further reading on Leo Brouwer:
Leo Brouwer - Wikipedia, the free encyclopedia
And the actual piece played by someone on youtube:
YouTube - La Espiral Eterna
I'm going to have to check later to see if the quality is good, but it should still give an idea of how it goes.