### Clue: Consider overlooking lake in uncontaminated part of Japan? (10)
### Answer: PREFECTURE 
 ### Explanation: Definition: part of Japan
 "reflect"(to consider/to think about) **minus**(overlooking) "l"(abbrev. for "lake") **contained in**(in) PURE(uncontaminated/clean).
Defn: One of the main administrative sub-regions/…