The best fit is Krasnodar Krai : it starts with C , has an area well above 500 square kilometers, is not landlocked because it borders the Black Sea, and it is generally regarded as one of Russia’s safer large regions.

Why this matches

  • Starts with C: Krasnodar Krai.
  • Area exceeds 500 km²: its area is listed at about 75,320 km².
  • Not landlocked: it has a coastline on the Black Sea.
  • Generally considered safe: among Russian federal subjects, Krasnodar Krai is commonly viewed as relatively safe compared with many other regions, especially for residents and visitors.

Quick note

If you meant a federal subject whose name begins with the letter C in English, Russian regional names are usually transliterated, so the closest practical answer is still Krasnodar Krai because of the “C” sound in “Krai” being a mismatch with the original naming convention.