The calculated distance (air line) between Castelnovo ne'Monti and Montignoso is approximately 31 miles respectively 49 kilometers.
By car or train, the actual journey to Montignoso is certainly longer, as only the direct route (as the crow flies) between Castelnovo ne'Monti and Montignoso has been calculated here.
Air line (approximately)
49 kilometers
27 nautical miles