Kolkata to Mandarmani distance is about 180 kms. The best option is to book a cab and enjoy the scenery along the way. One way cab booking gives you the best route experience. The ideal route would be via NH 16 and NH116B. This is the fastest route and takes about 4 hours despite normal traffic.
Mandarmani is a year round tourist destination. The best time for a Kolkata to Mandarmani getway is the the winters from October to February. The annual sand and surf festival is organised with much enthusiasm during the month of January. The summers(March to May) in Mandarmani like any beach destinations have hot days and relaxing nights. It is advisable to avoid family trips during monsoons(June to September) as the Bay of Bengal is known to be rough. In addition there might be cyclone alerts.
Kolkata airport is the nearest airport to Mandarmani. Outstation cabs are easily available from there. Digha is the nearest railway station. It has regular trains from Howrah. From Digha railway station one can hire taxi to reach the pristine beach resort of Mandarmani. Several buses as well as luxury buses are available from Howrah in Kolkata to Digha. From there you have to arrange for local transport. Mandarmani can also be reached via NH 16. This is however a longer route as it is almost 250 kms.
You can enjoy the ride with excellent roads till Contai and thereafter, the Street roads are somewhat narrow. However, with experienced drivers and cab services there is nothing to worry.