We present the STYX system, which is designed as an electronic corpus-based exercise book of Czech morphology and syntax with sentences directly selected from the Prague Dependency Treebank, the largest annotated corpus of the Czech language. The exercise book offers complex sentence processing with respect to both morphological and syntactic phenomena, i. e. the exercises allow students of basic and secondary schools to practice classifying parts of speech and particular morphological categories of words and in the parsing of sentences and classifying the syntactic functions of words. The corpus-based exercise book presents a novel usage of annotated corpora outside their original context.