Oh damn, still in this dream.

In what has memorably been called 'The_short_twentieth_century' the arts flourished in new ways. Narrative found new avenues for exposition; new media developed.

I suppose we ought to set the frame (and I quote pretty much the entirety of the wiki entry)

The short twentieth century, defined by Eric Hobsbawm, a British Marxist historian and author, refers to the period between the years 1914 and 1991.
That period begins with the beginning of World War I, and ends with the fall of the Soviet Union. These events represented such significant changes in world history as to redefine the era.

Anyway, Marxist historians aside (however memorable their coinage) the questions posed are thus: what are the greatest and most important works of art (or architecture) of any kind in the 20th Century. What things ought we to know of? What would we show some hypothetical alien cultural historian?

Seventeen years on we have had some small time to reflect, and we are also limited by the time-frame: so we just miss Stravinsky's 'Rite of Spring'.

The usual suspects would be likely to include the populist clichés, so here's a dozen to start the ball rolling:

Four_Quartets
Voodoo_Child (slight return)
Guernica
Fallingwater
Ulysses
The_Seventh_Seal
Side Two of Abbey_Road
Strauss's Four_Last_Songs
Bartok's String_Quartet_No._3
The_Wasteland
The Sydney_Opera_House
Citizen_Kane