Concert performed on January 24, 1975, at the Cologne Opera House, Germany. A logistical error resulted in a piano being provided that was unsuitable for the technical demands of pianist Keith Jarrett. A small piano with limited registers and poor tuning. Despite the adverse conditions and physical exhaustion, the performance took place in a completely improvised format. Creative exploration of the instrument's limitations. Result: one of the best-selling solo piano albums in the history of jazz and improvised music, becoming an aesthetic and cultural reference of the 20th century.
"...At the beginning, you can hear the murmur of the audience (the venue was sold out) when they realize that the musician is quoting the melody of the call signal. What comes next never ceases to surprise and move us. It's hard to believe that we are witnessing a set of improvisations without any prior structure."
Source: Jazz.in
We also recommend reading this article from Altamont.
https://altamont.pt/keith-jarrett-the-koln-concert/
