CASTLE ISLAND — Betty King and her friend Terry Carney had staked out their favorite spot and were watching the world unfurl before them.
Under a monument to a legendary 19th century shipbuilder, the two watched boats pass by — motorboats skimming the water, graceful sloops cutting through the wind — the fancy yachts.
“Look at that one,’’ oohed King, a 60-year-old who started coming to Castle Island as a teenager and grows fonder of it with every visit. “Yes, sir.’’
“I’m telling you,’’ Carney agreed, smiling at the sweeping scene.
A 22-acre state park in South Boston that juts into the harbor and features a commanding five-bastion fort, Castle Island has long ranked among the region’s most popular summer destinations, an urban escape that is close at hand, yet somehow feels far away, a spirited place that seems serene on even the most crowded days.
An attraction to walkers and runners who loop along the water in all seasons, Castle Island finds its glory in the summer heat, when its forgiving ocean breezes slice through the swelter and when ice cream at Sullivan’s, the famed snack bar, tastes all the sweeter.
At its peak, the park draws thousands of visitors in a single day, bustling crowds of picnickers, beachgoers, and fishermen. And the crowds are content to just sit back and take it all in.
“This is the best view in Boston, right here,’’ King said, her gaze moving from the downtown skyline across the water to Logan Airport and Deer Island. “It’s a beautiful, peaceful place. I could stay here all day.’’
All around them, the gentle whirl of Castle Island shimmered in the midday sun, like a slow-moving carousel. Children ran across the open field, then rolled down the grassy hill. Landing planes rumbled overhead, so low you could see the airline name and wave to the passengers.
Bare-chested men puffed their way around the loop, bellies hanging over belts, cigarettes hanging from lips. Elderly couples wearing Florida T-shirts and visors strolled together in silence, holding hands.
In recent years, Castle Island’s popularity has broadened, drawing families from far-flung suburbs and a polyglot of immigrants to complement an urban base that dates back generations. Today, the crowds are strikingly diverse, a demographic signpost of contemporary Boston.
Irish-Catholic families from Dorchester and South Boston share the shade with immigrants from Portugal. Fishermen from Brockton, Puerto Rico, and El Salvador cast lines shoulder to shoulder, hoping there are enough fish to go around.
“Nothing’s biting,’’ said Melvin Alvarado, a 38-year-old from Brockton who counts the Castle Island pier among his favorite fishing spots. But with the sun on the water and the wind on his face, no fish was about to spoil his day, he said.
“I’m relaxing, man,’’ he said. “All day long, right here.’’
Nearby, Rico Canas was having similar luck. The fishing used to be better at Castle Island, he said, recalling a day he reeled in 17 bluefish. Nowadays he is lucky to catch a handful.
But in other ways, Castle Island has changed for the better, Canas says. A native of El Salvador who moved to the Boston area in 1969, he used to see few Hispanics at Castle Island. Today, they flock to its enclosed bay and grassy hills overlooking the water from near and far.
“Everywhere you look,’’ said Canas, 62. “It’s a good thing to see.’’
Up the hill toward Fort Independence, Linda Breen of Hull looked out over the harbor. Breen, 58, has been coming to Castle Island since she was a girl, and in her mind’s eye could still see the kite of her childhood floating in the breeze and could almost taste the picnics of cold chicken and potato salad.
Castle Island is a unifying force, Breen said. No matter where you come from, you come here for the same reasons.
“The fresh air, the water, maybe something at Sullivan’s,’’ she said. “We all kind of share that.’’
Many people who have been coming to Castle Island for years say its popularity is at an all-time high, as suburbanites stumble upon its secret, while those who went to Castle Island as children introduce it to their own.
“People seem to be coming back to what’s familiar to them,’’ said Jackie Cusack, an 81-year-old from Norwood, as she walked with her family. “It’s just a great time. There’s everything here.’’
Sharon Carrigan, a 65-year-old from Arlington who has been coming here to the harbor’s edge for four decades, said the crowds have grown steadily in recent years and the park’s popularity is infectious.
“It’s a place for anybody and everybody to enjoy,’’ she said. “I love to watch the people enjoy their time here.’’
As she prepared to leave her coveted spot for a fish sandwich and crinkly fries at Sullivan’s, King remembered the days of the school busing crisis when she and other African-Americans could not feel comfortable at Castle Island.
When she returned, she had forgotten how much she missed it. But no longer.
“It’s for the best,’’ King said. “Because this view is for everybody.’’
Globe correspondent L. Finch contributed to this report. Peter Schworm can be reached at firstname.lastname@example.org. To read other articles in the series, go to www.boston.com/news/local/breaking_news/summer_in_the_city.
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