For seventeen summers, the most beautiful building on Jones Beach was locked.

Anyone who walked the East end of the boardwalk after 2009 saw it: a long, pale, monumental thing with stone towers and a courtyard, sitting there in perfect view of the Atlantic and completely off limits. Fences, plywood, weather doing what weather does. It was the sort of building people assumed would eventually be quietly demolished.

Instead, the East Bathhouse has just reopened after a $100 million restoration, and it has come back with something Jones Beach has never had in this spot: a zero-entry learn-to-swim pool, 125 feet by 75, and a sprayground built for small children. Free youth swim lessons begin Wednesday, July 29.

What Robert Moses built here

Jones Beach State Park opened on August 4, 1929, dedicated by Franklin D. Roosevelt, who was then the governor of New York and three years away from the presidency. The East Bathhouse followed in the spring of 1930, designed by architect Herbert Magoon in a mix of Beaux-Arts and Art Deco that has aged better than almost anything built on Long Island since.

It was enormous, 115,000 square feet, and it was built for a world that no longer exists. In 1930 most people did not arrive at the beach already wearing a swimsuit under their clothes. They arrived in street clothes and needed somewhere to change, so the bathhouse was organized around a central courtyard lined with cabana-style changing rooms, with an entrance building to the north and a second building to the south.

The details were not incidental. The south building had a long central promenade running the full length of its first floor, deliberately borrowed from ocean liner design, plus a sun deck and a canopied terrace. There were concessions and there was music. It was not a place to change your clothes. It was a place to spend the day.

And on its stone towers were two bronze clocks, side by side. One told the time. The other told the tide.

How it went dark

The building was heavily reworked between 1967 and 1970, expanded to 150,000 square feet, with the original central block demolished and replaced by a large pool with a diving area plus a smaller wading pool. New wings went up. Enclosures changed.

Then came thirty-five years of deferred maintenance, and in 2009 budget cuts closed it entirely. A salt-air building with no one in it deteriorates fast.

What is inside now

The restoration was funded through NY SWIMS, the state initiative that its backers describe as the largest investment in public swimming infrastructure since the New Deal: nearly $260 million across 79 projects statewide.

The North and South Bathhouse buildings have been rehabilitated and now hold park offices, first aid, concessions, accessible restrooms and family changing areas. The work preserved the original materials rather than replacing them, which is the expensive way to do it: Barbizon brick, Ohio sandstone, bronze, woodwork and the decorative mosaics.

The pool is the headline. Zero-entry means it slopes in from the deck like a beach rather than starting at a wall, which is the single most useful design decision you can make for a child who is not sure about water yet. Next to it is a sprayground themed to the park's own iconography, with custom water elements shaped as seahorses, the Jones Beach emblem, along with whales, dolphins and classic Jones Beach boats.

The lessons, and why they matter

Youth lessons start Wednesday, July 29, for ages infant through 15, running between 8 and 10 a.m. and grouped by skill level. Adult lessons run Thursdays from 7 to 7:45 p.m., which is a genuinely uncommon offering; the number of adults on Long Island who never learned to swim is larger than most people would guess, and an evening class for grown-ups removes the part that keeps them away, which is being the only adult in a pool full of eight-year-olds.

State officials cited the figure that swim lessons have been shown to reduce drowning risk by as much as 88 percent. On an island where every town is within a short drive of an ocean, a bay, a sound or a pool, that number is not an abstraction.

Through Labor Day the pool runs weekdays from 10 a.m. to 6 p.m. and weekends and holidays from 9 a.m. to 7 p.m. Vehicle entry to Jones Beach is $10 while the beach is open. Pool admission is set separately and the state has described it as deliberately budget-friendly; check parks.ny.gov for the current rate before you go, and note that lesson registration for state park learn-to-swim programs is typically handled on site rather than online.

There is something worth noticing in all of this beyond the amenity. Long Island does not often get its grand public buildings back. Usually the ending is a parking lot. This one got seventeen years of neglect and then a hundred million dollars, and the bronze clocks are still on the towers.