It isn’t summer, or the end of it, until I’ve been to the beach. I don’t mean a beach by a lake, where the waves loll and it’s mucky underfoot and you can see weeds growing on the bottom. Nor do I mean the bayside beach where we sometimes go, though that’s pleasant enough. I need an honest ocean beach, with white sand dunes and a sea breeze that snaps the lifeguard’s flag, where your hair gets salty just sitting there and the surf slams and tosses foam and reminds you that there’s nothing but sea between you and Normandy.

My kids are fascinated and frightened by this sort of beach, as they should be, but I knew that summer had arrived in an eternal sense last year when they came to love it. This was Labor Day weekend, that radiant diapause between languor and regiment, when the days shed their names and briefly hint at endlessness. A hurricane had come and gone, leaving sun and froth. My boys, who were both five, spent the early part of an afternoon learning how to be properly dashed by waves—such that seawater streams from your nose. Then the tide started going out, and it was time to build sand castles.

Here is an essential human pleasure: to fill your hand with sand, turn it over, and call it architecture. We picked a spot at the lowest sustainable point below the tide line. It was prime floodplain real estate—flat, with perfectly moist sand—but also, I knew, high risk: our work would be the first to fall when the tide returned. In only a few minutes, one boy had flung together a hamlet of sand mounds protected by a low, curving wall. I dug a moat in front of it, to slow the first waves when they came, and built a break-wall in front of that. My son looked on with gleeful amazement. “We’ve never had this much time!” he declared with delight. He meant, I think, that he had never been so close to the waves—the tide was still receding—and yet able to accomplish so much. I noticed the younger parents higher up on the beach. “Look at our little town,” my son said, impressed by his industry and that its products still stood. He exclaimed again, “We’ve never had this much time!”

Nietzsche once argued that you can gauge a man’s relationship to time by the way he builds a sand castle. The first man, he wrote, will proceed hesitantly, intent on craft, fretting all the while about the inevitable return of the waves and shocked by his loss when they finally arrive. A second man won’t even start building: Why bother if the tide will only destroy it? The third—the paragon of manhood, in Nietzsche’s view—embraces the unavoidable and throws himself into the work regardless, joyful though not oblivious.

I would like to think that I belong to this third category, but I see myself all too keenly in my other son. Against my gentle recommendation, he had started his own construction project—a small mound that he had patted and sculpted into some elegant shape—beyond the protective wall of the sand town. The first errant wave reduced it to a wet lump, and him to tears. He started a second hermitage, which crumbled, then a third, also outside the walls. By then the tide had turned. The waves crept up the beach; he was the first casualty exposed. A wash of water swamped his outpost, and kept advancing. Waves overran my break-wall and my moat and lashed the wall of the town itself, then they curled behind the wall and flooded the streets in a grainy surge.

“The end is here! The end is here!”

The first boy stood behind the ramparts facing the tide, his arms outstretched, the grin of ages on his face. He was a giant. He had never looked so happy, and I envied him.