Appleton and Jones' 'Puer Romanus'.
Appleton's reader is suitable for a 21st century intermediate student of Latin, although even a beginner will benefit from extended oral input in the language. The reader is in the form of a novella, told from the perspective of a young Brundisian boy, called Lucius. This books is justifiably famous - and remains one of a handful of such texts ever written.
Puer Romanus
4 hours 16 minutes of audio
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More information about Latinum can be found at Latium Redivivum ,
including lists of the material graded by ability level.