Head to Amakusa,drive over the "famous" 7 bridges and towards Hondo. From Hondo, drive south on the 266. Take the signposted right for Takahama. After a 30 minute drive you will reach the coastal road. Turn left and then follow signposts to the beach.
Park in the dirt car park close to the graveyard. When they charge for 2 weeks a year just park on the road.