It took nearly four years to conceive and build a theme-park ride that put visitors inside the world of "The Little Mermaid," including several musical numbers, a few key narrative moments and 184 figures from Disney's animated hit.

And that followed the 18 years it took to settle on an approach to the ride, which was on the entertainment giant's to-do list almost from the day the film was released in 1989. The ride finally opened last week at Disney California Adventure, Disneyland's younger neighbor, and takes visitors through a condensed version of the movie's narrative, cramming nine scenes and four songs into 5½ minutes.

The creative force behind the ride is a team of three veteran Imagineers (as Disney calls the people who design and build its theme parks, rides and attractions). They spearheaded a group of over 100 designers, architects, lighting experts and other specialists to build "Ariel's Undersea Adventure."

Two members of the team, Larry Nikolai and Chris Crump, have worked together for 15 years—the last four of them on the Ariel ride and, for more than a decade before that, on pieces of the DisneySea theme park in Tokyo. The third, Lisa Girolami, began working with them at the beginning of the Ariel project, after stints in film and multimedia production.

"We're kind of like an old married couple," said Mr. Crump, 56. "I know what Larry does. Larry knows what I do."

Mr. Nikolai, the lead designer of the ride, bears a passing resemblance to Mr. Crump and is also 56 (Ms. Girolami joked the two are "twin brothers from different mothers"). Mr. Nikolai is responsible for the initial drawings, and for populating the ride in ways that felt faithful to the original movie.

"Larry really focuses on the characters and I really focus on the setting for the characters," said Mr. Crump.

Like an old married couple, Messrs. Crump and Nikolai aren't above a little bickering. Asked how much he tries to ensure that his early designs are likely to be physically possible, Mr. Nikolai found himself interrupted by Mr. Crump chortling: "He doesn't!"

"As a designer, you always start with the aesthetic and the composition of the thing," Mr. Nikolai elaborated. "But both Chris and I have over 30 years' worth of experience in these shows, and we've learned that you have to stay flexible."

Helping the duo stay flexible is part of the role played by Ms. Girolami, 50, the ride's producer. Her job, she said, is to support the other two and give them everything they need (assuming, that is, that what they need falls within budget, time and space constraints).

One big challenge faced by the group was making Ariel's hair move properly. Eventually, they found the solution by looking back to the ride's roots. They turned for guidance to Glen Keane, the lead animator on the original film, who still works in Disney's animation building in Burbank, about 30 miles from Disneyland.