Believe it or not, there are no roads that link the Atlantic Coast of Nicaragua to its inland interior. The only form of transportation open to you is by water and air. The easiest way to journey to Nicaragua's Atlantic Coast is by air. The "Atlantic Airlines" and the "Costeña" link Managua with Bluefields, Corn Islands and Bilwi, the cost of a round trip tiket is about $100.
If you dont want to fly to Bluefields you go by bus to Rama; you catch the bus in Managua at the Mayorero bus station. The bus can go no further because this is where the road ends and the marsh begins. From Rama you must take a small boat that goes down the Escondido River to Bluefields. The complete trip takes about 6 hours by bus and another hour and a half by boat. Total cost is about $15 one way.
You can get to Puerto Cabeza by car, however, it is not for the faint of heart. You have to cross Matagalpa, Rancho Grande, Suina y Rosita or Boaco and Rio Blanco is prefered for the paved road. It's a long trip, about a day and half and you are traveling in some very primitive undeveloped areas. You must carry extra gasoline, food and water because town are far apart and you can drive for some time before you see anyone else on the road.
If you like traveling by car you must use a 4 wheel drive vehicle and it is best not to travel during the rainy season. There are buses that run between Managua and Puerto Cabeza, however, the trip is very long.