The allure is undeniable: The gleaming blue lagoon, sparkling in the sunshine, holds 9 million gallons of water, with vibrantly colored sea life just below the surface. Vivid yellow submarines glide across, halfway submerged, disappearing into a yawning cave covered by a churning waterfall. Above, the Disneyland Monorail glides overhead into the Tomorrowland station.

Finding Nemo Submarine Voyage is an underwater boat ride that puts guests onto a research submarine operated by the “Nautical Exploration and Marine Observation Institute,” or N.E.M.O., to find the little missing clown fish from Pixar’s 2003 film “Finding Nemo.” Along the way, through the portholes of the sub, riders see the ruins of ancient civilizations, scuba divers and characters from the movie including Marlin, Dory and, of course, Nemo himself.

The ride is perennially popular. According to Thrill Data, Finding Nemo Submarine Voyage has an average wait time of about 30 minutes, well below the park’s most popular rides but solidly in the center of the rankings. It’s also one of the park’s oldest and most historic attractions, using the same submarine boats installed in 1959 for a ride called Submarine Voyage.

Its age and maintenance difficulties have put the underwater voyage at the center of some of Disneyland’s most intense internal debates. In 1959, the ride was a marvel unlike any other theme park attraction, partly inspired by “20,000 Leagues Under the Sea” and partly by the USS Nautilus, the world’s first nuclear-powered submarine, which voyaged to the North Pole in 1958. Walt Disney described the 52-foot-long boats as “the eighth-largest submarine fleet in the world,” according to the Los Angeles Times, and naval officers attended the ride’s opening ceremonies.

But like so many attractions in Tomorrowland, the technology of the future quickly became a thing of the past. People’s attention waned, and the ride became burdensome because of costly maintenance. By the 1980s, the LA Times wrote, the lagoon was leaking thousands of gallons of water a day.

Disneyland officials had been gutting old Tomorrowland attractions such as the People Mover in favor of modern ones such as the ill-fated Rocket Rods, and Submarine Voyage was on the chopping block. But Imagineers (the creative team behind Disney attractions) were adamant that the ride be preserved. Walt Disney World’s version had already been closed, the land used only as a play area and meet-and-greet spot for years until becoming Seven Dwarfs Mine Train.

Disneyland’s version, if the creatives had a say, wasn’t going anywhere. Too much of Walt Disney’s Tomorrowland had already been lost. The LA Times reported that Marty Sklar, the head of Imagineering at the time, “publicly threatened to lie down on the busy street that fronts Disneyland to prevent the subs from being deep-sixed.”

“Oh, I said it,” Sklar said in 2007. “I meant it. I’m sure glad I didn’t have to throw myself across Harbor Boulevard. I never gave up.”

Submarine Voyage closed in 1998, but its fate was uncertain. Imagineers kept fighting for the ride, a rare instance of creatives and executives clashing in the public eye rather than behind the scenes at the company. Imagineers Bruce Gordon and Tony Baxter put up an unauthorized sign that read “Atlantis Expedition Imagineering Preparation Base” outside the closed attraction, leading to wide speculation that it would be rethemed.

“Everybody that could throw themselves in the way [of closing the ride] obstruct it, block it, or stop it did,” Al Lutz, told the LA Times in 2007.

Because of those efforts, officials relented in keeping the lagoon and retheming the ride. The deciding factor was when Sklar hired a naval engineering firm to assess the submarines. According to Sklar, they “came back and said, ‘Fellas, there’s 40, 50 years life left in these things.’”

The lagoon was an empty eyesore for nearly a decade, until reopening with a “Finding Nemo” revamp in 2007. The refurbishment changed the show experience and converted the boats from diesel to electric, thereby making space for two more seats per vessel, for a total of 40 passengers each. With the additional seats, the ride can accommodate around 1,000 people per hour, compared to rides such as the Haunted Mansion and the Pirates of the Caribbean, which can take in, respectively, around 2,600 and 3,400 people hourly. To meet initial demand when the ride opened in 2007, the park announced that “Finding Nemo will remain open for up to 2 1/2 hours after the park closes, adding up to what Disneyland calls an ‘eighth day’ in the week,” the LA Times wrote at the time.

Aside from new paint, new names and those additional seats, the submarines were, and are still, largely the same as they had been nearly five decades prior.

That historicity is the root cause of the ride’s biggest problem, even today: The boats were designed in the 1950s for people without disabilities and didn’t account for people with size differences. They’re difficult to board for those with even mild mobility issues. Once you step from the dock onto the top of the sub, you have to descend a narrow, steep staircase down inside, and then navigate a constrictive space to get to your small seat.

It’s a tough ride physically for those who aren’t easily able to manage stairs, who have size differences or who struggle with being confined in small, dark spaces. For people who can’t transfer from a wheelchair or an electric conveyance vehicle, getting into a sub is a nonstarter. But there’s another way to experience the ride without having to get into a boat.

The Marine Observation Room is an above-water space where you can see the show, which is tucked into the ride queue. To access it, ask a cast member at the entrance to the ride, and you’ll be guided over to a small waiting area. Inside the room, there’s seating, ample space for wheel-based conveyances and blissfully icy air conditioning. There’s also a large screen: The cast member who starts the show will turn off the lights, and the “underwater” show will play as you sit, cool off and watch the entertainment.

As Disney describes it, “For those unable to navigate the narrow steps down into the submarine, you can proceed to the Observation Outpost at the end of the dock. Manned by a member of the N.E.M.O. Institute, this facility offers a high-definition, live-feed video version of the voyage via onboard ‘SubCam.’”

Once the show’s over, the lights come back up. Before you leave, take a minute to enjoy the decorations in the room. There are lockers filled with dive equipment, as well as photos of Finding Nemo Submarine Voyage cast members over the years, some dating back to the ride’s opening day. It’s a sweet glimpse into a facet of the Disneyland experience not normally accessible to guests and for those of us who would rather not squeeze into the submarine, it’s a delightful alternative to the original ride.