Jorge Tiscornia, a member of the MLN-Tupamaros, kept the diary (known as "El almanaque" in Spanish) during the 12 years he spent in prison during the 1970s and 80s, hiding the papers in a pair of hollowed-out clogs.
In a statement, Unesco said it was "a living memory of long isolation, revealing the strength of perseverance".
An amazing document.
Uruguay prison diary preserved by Unesco (BBC)
Almanaque de ex preso uruguayo declarado patrimonio por Unesco (El País, Uruguay)