undecidable problems in Euclidean geometry

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What is (are) the most "elementary" question(s) one could ask in Euclidean geometry with all its postulates/axioms including the "5th" that is (are) known to be undecidable. The "5th" is undecidable by the rest but Godel says even if we include it there will be something else. What would be the next simplest question one could ask in the axiom system with the 5th that cannot decided? I am looking for questions that are simple, intuitive, visualizable so I could show it to a 10 years old as an example.