Susuki [須須木] beach, one of my local favorites, is about a 6 km drive south on Route 150 from popular Shizunami beach on the Sagara coast. The beach, behind a tree-lined rise and below the dunes, is not seen from the road. After passing Sun Beach in Sagara, there are several places to turn in to your left with ample roadside parking.
Unlike some summer beaches which are overly-controlled and roped off to postage-stamp size, Susuki is wide-open and swim at your own risk. The bottom however is sandy and sloping, there are no serious rip tides, and it is generally safe for kids.
Adults need to employ common sense and practice standard beach etiquette, e.g. if someone is there first, i.e. a fisherman or a surfer, try not to interfere. Susuki is wide enough to accommodate. Jet-skis are mercifully few, so when you hear one coming, watch out for it. Fisherman will occasionally show up early and leave by late morning.
About half of Susuki is 'protected' by the ubiquitous tetrapods, those four-legged concrete structures that look like jacks that kids played with before there was TV. Tetrapods are used to build seawalls that dissipate wave force and arguably prevent erosion. Their effect on the waves there is to slow them a bit, push them up and funnel them.
Surfing can go on all day depending on conditions. Generally the waves are rights and break fairly close to the beach. I found this out the hard way. Once during winter surfing I was frustrated by conditions and tried to cheat a ride in close and, for the second time in my inglorious career, got pounded onto the bottom. Beginning the prolonged cedar-tree allergy season with a cracked rib is no way to go, and I was sorely reminded of my egregious error every time I sneezed. Remember: sloping bottom, if you decide to surf there.
It is no secret that Japan is at times battered by the effects of typhoons and Susuki is no exception. The upside is: that with its extensive sandy beach, Susuki is an excellent place for beachcombing. I have developed a nice shell collection from there.