It's possible to take a 4WD from Playa Carrillo along the southeast coast to Islita, Playa Coyote and south to Mal Pais.
From Playa Coyote, you'll cross a few rivers, including the Rios Bongo and Ario and pass Playas Caletas, Ario and Manzanillo. This dirt road doesn't cross the rivers perfectly, so you'll need to drive up river to find suitable crossings. Consider walking upriver to assess the crossing and double-check the egress so that you don't plunge into the mud. You probably won't find anyone to pull you out of the mud, so be sure to find the right crossing.
From Playa Manzanillo head inland to Cobano which is well connected by dirt road to Montezuma and Cabo Blanco.
For the majority of the trip, there are no facilities. There are no signs. Be prepared to survive on your own, so bring food, water, compass and jerry can of gas. You might consider brining a rope or chain to pull yourself out of the mud (in the event, you don't assess the egress properly).