Indecipherable (adjective)

1. Impossible to read or understand; unreadable.
2. Impossible to interpret or explain; mysterious.

Origin:

From in- + decipherable.

Examples:

1. The ancient script was indecipherable to the archaeologist.
2. The handwriting on the note was indecipherable.
3. The scientist found the indecipherable data difficult to analyze.
4. The indecipherable message was assumed to be a code.
5. The indecipherable symbols on the map were thought to be a secret message.