Summer means ice cream, baseball, sand castles and mini golf — and the clock is ticking down mighty fast. So in the spirit of wringing every last bit of fun out of the season, we’re heading out to do all the classic things … but with a twist. Because if one ice cream scoop is good, eight scoops smothered in eight toppings with a side of windmill mini golf and splashy river swimming is even better.

Hot and sticky? You don’t need a swimming pool when California is full of lovely rivers, lakes and beaches. If you’re seeking inspiration on where to enjoy au naturel swimming — and yes, that sometimes means clothing’s optional — take the advice of Caroline Clements and Dillon Seitchik-Reardon, authors of this year’s “Places We Swim: California” (Hardie Grant Explore, $35).

Seitchik-Reardon and Clements are Australian writers who traveled across the state in an old RV to dip tootsies in the most scenic gorges, waterfalls and hot springs. “We loved winding through the redwood forests in Northern California to find glassy, freshwater swimming holes along rivers,” says Clements. “Then driving hours and hours into the desert to find ancient hot springs. California is truly such a diverse state, and we’ve really tried to capture that in the book.” (Follow them on Instagram at @placesweswim.)

Their favorite swimming spot in the Bay Area is beloved for its pristine water and secluded scenery: Gualala River Redwood Park (46001 Gualala Road, Gualala; free with a nightly camping fee). “From far off, (the river) looks like a shimmering green mirror,” they write. “Up close, the water is so clear, it’s impossible to gauge its depth. Salmon glide past far below the surface, and you can easily count individual stones in the riverbed.”

Another swim that impressed was near Healdsburg in Del Rio Woods Regional Park (2656 S. Fitch Mountain Road; $7-$10 parking fee), where you can tube down the river with a floating cooler. “It’s a migrating picnic, where each sandy beach or gravel bar is better than the last,” they write. “We sit under pale green willow trees or sunbathe on warm pebbled beaches. Mostly, though, we relax in waist-deep water, a book in one hand and a beer in the other.”

Sunny Cove near Santa Cruz was their top pick for beach swimming around the Bay (on Sunny Cove Drive in Twin Lakes; free). “On a clear day, the cove reminds us of those narrow calas in Majorca,” they write. “Flat reef extends around the base of the bluff, and people leap into the water below, timing their jump to hit the top of incoming waves. Kids squeal with delight as the water chases them up the beach.”

The authors recommend packing in water, food, sun protection, trash bags, a pocket knife, a good book — and a sense of respect. “Don’t be a jerk and don’t leave a mess behind,” says Clements. “Ultimately, be respectful and considerate of these shared spaces and the locals who love them.”

But wait, there’s more >> In search of a more luxurious swim? Consider Resort Pass — www.resortpass.com — an OpenTable or Resy but for hotels who offer day passes for their pools and other amenities without the overnight stay. Among the possibilities: a day pass for Santa Rosa’s Flamingo Resort & Spa ($54) and pool access at Napa’s swanky Stanly Ranch ($109-190). Luxuriate a while, pretend you’re a celeb on the A-list, then slip out with enough time to grab Burger King for dinner.

When Adam Richman, erstwhile host of the Travel Channel’s “Man v. Food,” came to town in 2009, he knew exactly where to go for an over-the-top dessert: The San Francisco Creamery in Walnut Creek, home to an immensity of sugar and frozen cream called the Kitchen Sink.

This towering sundae ($76), estimated by Richman to contain two gallons’ worth of sweets, includes eight scoops of ice cream, three bananas, whipped cream, nuts and cherries and eight toppings, including hot fudge, candy and Oreos. Anyone who eats the whole thing in less than 30 minutes gets a prize that seems demented, in a Homer Simpson doughnuts-in-hell type of way: free ice cream for a year. To date, co-owner Terry Wong says, about 1,600 challengers, many of them competition-circuit eaters, have vied for the prize — roughly 30 have succeeded.

Wong says it takes him only a few minutes to figure out who will finish, given their spoon pacing and chewing techniques. (Tip: Don’t let the ice cream melt in your mouth; swallow each spoonful whole.) The staff still talks about the guy who ate not one, but two Kitchen Sinks in one sitting.

“He let us feel his stomach. He had rock hard abs, and they were freezing cold,” Wong says. “That was the most gnarly thing I’ve seen.”

It helps that the creamery serves quality ice cream, churned on site, with fudge and brownies made with local Guittard chocolate. Richman liked the sundae so much, he finished it in 45 minutes. The all-time winner, though, was a skinny-looking blonde woman from Plumas Lake who did it in 6 minutes, 41 seconds. Wong still sounds impressed: “She just inhaled it.”

The details >> Fortunately for the rest of us, the creamery offers regular-sized sundaes, as well as lunch and dinner items. Open Tuesday-Sunday at 1370 Locust St., Walnut Creek; sanfranciscocreameryco.com

But wait, there’s more >> The South Bay is full of classic ice-cream parlors, with trip-worthy destinations such as Sweet Retreat (sweet-retreats.com) in Morgan Hill and San Jose, Willow Glen Creamery (jeffswillowglencreamery.com) and the gelateria Dolce Spazio (dolcespazio.com) in Los Gatos. And closer to the Peninsula it’s hard to go wrong with Asian flavors and fish-shaped cones at SomiSomi (somisomi.com) or the artisan ice cream at The Penny Ice Creamery, known for its torched-marshmallow fluff (thepennyicecreamery.com). Elsewhere in the East Bay, folks might want to try the towering soft serve at Meadowlark Dairy in Pleasanton (themeadowlarkdairy.com) or the fruit-infused treats at cult pop-up De La Creamery (delacreamery.com) in Oakland.