The Most Challenging Prog You've Ever Heard

I'll mention 3 examples of what I find challenging :

1. Universe zero - Heresie. This is a very classic oriented album with very dark atitude. It is quite obvious that it is good, rich, complex and deep but I need to be in a very optimistic mood to dare to put it on.

2. Henry cow - Western culture. Very dysonant. Beautyful to my ears but needs very devoted hearing. What's funny is that "In praise of learning" is very listenable IMO.

3. Pink floyd - Ummagumma. After quite a few listens I still do not understand it so I can't realy say if it's good and chalenging or does not make sense (and I find "Saucer full of secrets" an accesible album so don't ask me what's the difference. I don't know myself).

Don't you just love it when someone jumps in with a condiscendent reply, assuming you're an idiot? I know I do.

So now I need to explain my position. 

If we talk about paintings, I guess there is little to no doubt that Caravaggio's Beheading of St. John the Baptist makes more sense as a painting than, I don't know, Fontana's cut. So, while talking about "meaning" in absolutistic terms doesn't make much sense, you certainly can talk about meaning in relative terms. Fontana's cut has close to no meaning at all when you compare it to a painting by Caravaggio. It's not inaccessible, it's just a terrible, terrible excuse for a painting, if you analyze it AS a painting. Its significance goes well beyond that. 

Now, one can safely say that Fontana's cut is like farting for 50minutes on a cd. If it has a meaning, it's not, or at least not mainly, about music. If we listen to this, for example:

Henry Plainview wrote: Otomo Yoshide [sic] probably has the most challenging discography on here. Consume Red is 5 second sample looped for 45 minutes, and Cathode is high pitched droning sine waves.

I am with you.

 

Could not agree more. I reckon i'd absolutely love the band if i could stomach the singing

 

The word "challenging" to me indicates that there is some kind of enjoyable pay-off for taking the effort to appreciate the music.  It may be difficult to hear all of what is going on, or to get an understanding of what the artist is trying to convey.  As far as rock is concerned, I would say Gentle Giant.  Their music is so intricate I have to listen several times to even hear all of what is going on.  Beyond that is the fusion music of Miles Davis, especially Bitches Brew.  There are so many layers to the music that it sounds almost like different pieces every time I listen.  The same is true for his Tribute to Jack Johnson.  Two of Herbie Hancock's albums, Mwandishi and Crossings, have similar depth.  In another way, The Residents are a challenge in that they have created their own musical language that is consistent with itself but not much with anything else (nor is it simply noise).  All of these example fits my criteria - I took up the gauntlet, listened attentively, and came to a deeper appreciation for music because of it.  These artists challenged my conventions of music, and I enjoy them all.