REACHING THERE- From Kolkata via Kona Expressway, via Mumbai Road to Kolaghat. Then Contai. Take Digha route. On the Kolkata-Digha road reach Chawlkhola. Be sure to ask directions, the left turn from this road is almost impossible to find unless you are looking for it very carefully. Once you leave the Kolkata-Digha road, the paved roads end and the bone rattling drive for 10 kms begin. Keep asking directions every few minutes. If you survive that drive, you will reach the beach and will have to drive on the beach itself for a good 4-5 kms till you reach your resorts. The beach drive can be tricky, at high tide this bit is submerged and vehicles might have to wait for the low tide. If availing public transport and Kolkata- Digha bus will drop you at Chawlkhola from where local transports are available. (Trekkers where you can hang on for dear life on the stretch). Its worth the trouble when you see the beach.
Go to this link for the wiki map of the area- http://wikimapia.org/510487/
STAY- Resorts line this beach, pick one according to your pocket. We stayed at the Sana Beach Resort. It was expensive, but very nice. Rooms were tasefully decorated, with AC, the reception area is huge and well decorated too. The food isnt bad either.
WHAT TO DO- Loll around on the beach. Some resorts have their beach beds, with umbrellas and towels. There are shacks where you will get simple yummy crab curry (they will make it for you if you order), prawns, beer, bread, eggs, packaged water and soft drinks. People drive on the beach, but ideally its not recommended due to the ecology of the area. You can walk/drive toward Digha on the beach itself until you reach a river cutting through to the sea. Its shallow enough to wade into, deep enough to have a small ride if you can convince a local boatman. We did. The resorts also have good game rooms or pools.
FOOD- As long as you keep the money flowing, there will be no dearth of food or drink. Vegetarians will have a problem, will have to stick to biscuits and bread-butter on the beach, or else get from restaurants of the resorts. All the resorts have their own restaurants.
You can google Mandarmani for more information. Lots of it available, including photos. For photos go here - http://www.trekearth.com/gallery/Asia/India/East/West_Bengal/mandarmani/