Don Goldstone didn’t know what he was getting into when he visited a client in Hidden Hills, Calif., in 2005.

He just figured he would finish another builder’s work.

But the previous contractor had only dug out part of the yard and begun some artificial rockwork before leaving the site.

The client gave Goldstone carte blanche — as long as he could produce the biggest and best of everything.

“His original budget was $600,000,” says Goldstone, president of Ultimate Water Creations in Los Angeles. “I told him that he could get a phenomenal pool for $600,000, but not what I was going to design. If he was going to let me go wild on it, it would be a lot more than that.

“I asked, ‘Do you want me to bother, or should I just stick within the $600,000 range?’” Goldstone recalls. “He said, ‘Give me the best and let me decide.’”

Nearly two years and $2 million later, Goldstone had created a 10,000-square-foot, two-story megaproject, the job of a lifetime, a tropical-themed, resort-type pool in Goldstone’s signature large-scale artificial rock. He dug out the existing artificial rock and created his own behemoth, meant to look as if it had formed naturally against the hillside.

“If you’re digging into a mountain like this, what else would you have except a cave of some type?” he says.

Three major areas — a large, beach-entry pool, 20-foot-tall cave and the cave’s roof — answered the client’s desire for as many “fun amenities” as possible. Seven plasma TV screens, numerous speakers (standard and underwater), and color-changing LED lights add to the festive atmosphere.

Enjoy this tour through his masterpiece.

The Oasis

The main pool is chock full of interactive features, including a swim-up bar with a complete kitchen in back and a poolside blackjack table with seating for five.

“There are five seats at a normal blackjack table, and he wanted the granite engraved with playing cards just to make it interesting,” Goldstone says. “Then there’s a square box for a dealer.”

A fireplace and accompanying dry bar were placed nearby. Because the project also had to blend in with the brick, ranch-style home, Goldstone used stacked stone for the fireplace, kitchen and bars.

The approximately 75- by 60-foot pool includes depths ranging from a zero-entry beach to a 14-foot diving well.

“So if someone were to jump off the grotto, they wouldn’t get hurt,” Goldstone says.

He finished the pool with three colors of aggregate material to denote depth changes, with the colors growing deeper with the water (above). His staff then feathered the colors together where they met to create a blending effect.

On the other side of the pool is an island, accessed from the deck by a bridge. A fire pit sits in the center. Originally, the homeowner wanted a permanent bench around the island. But after the bench was formed in concrete, he changed his mind.

So Goldstone and his team filled the island’s floor with concrete to even out the elevation. Now padding covers the island around the fire pit; but it can be removed to accommodate a table and chairs.

Inside the pool, 14 color-changing LED lights were strategically placed to illuminate the island and its many bar stools, and to prevent dark spots. A moonlight flagstone covers the deck and beach entry.

Not-So-Secret Cave

The gigantic cave, measuring approximately 400 square feet, can be accessed by land or water. Goldstone is particularly fond of the swim-through access, with two entries beneath massive waterfalls.

“I wanted just the romance of it, the uniqueness of it,” he says. “There are gas torches inside so when you’re swimming by them, you get the reflection of the flames on the water.”

Inside, the cave features a 9-by-14-foot spa, a poolside bar and plenty of seating. The client wanted to view movies on a sheet of water, so Goldstone installed a mechanism that creates a waterfall for that very purpose.

“It’s basically a 4-inch copper tube that has a series of three jets lined up in a row,” Goldstone explains. “[The jets] have little tips on them that make them perfectly straight.”

It’s powered by two 2-horsepower pumps, with one on either end of the apparatus. Special filters strain tiny particles so they cannot enter or clog the jets.

A spiral staircase leads from inside the cave to the second level. The iron staircase was designed to look like a tree, with steps along the “branches” and handrails that resemble vines. Goldstone’s crew set pieces of flagstone on top of metal treads that came as part of the staircase. Then they lined the stairway’s opening with rockwork.

“It was interesting, but it was also done because of space,” Goldstone says. “We had to get up a total of about 25 feet vertically. We would have needed about 40-something feet for a conventional staircase, which would have taken up a huge amount of room in the cave.”

Rooftop Getaway

The top level of this aquascape is a world of its own. A stream runs from one end to the other. It’s where most of the plants were placed. Planter pockets and floating artificial rocks add to the stream’s texture.

“Those areas of plantings were a combination of many planter pockets with sprinklers, lighting and drainage,” Goldstone says. “Then there are areas where we left large openings and the original soil, [so] we could plant big trees between the waterfalls.”

A second 9-by-14-foot spa is perched on one end. “It needed to look like a little pond,” Goldstone says. “It had to look natural, but also be comfortable. So we didn’t want to make the rock too jagged and irregular.”

Amid the serenity are plenty of high-energy activities, including a 100-foot-long water slide that winds through the immense rockwork. It’s virtually invisible from all angles except the entry and exit.

“It just looks like another grotto opening,” Goldstone says.

Made of concrete glazed in a brown tone, the slide was tested on site to ensure the sides were deep enough to contain any swimmers sailing down its curves.

“We had to make several adjustments in the finished product once we had tested it,” Goldstone notes.

The team even set up a camera at the bottom of the slide and a monitor at the top, allowing users to check that the coast is clear before entering the slide.

The upper deck also holds a bandstand, ping-pong and pool tables, and a sand volleyball court.