“I feel like it’s a little city down here, tucked away from the world.”

Debbie Krumboltz, a real estate agent from Mission Viejo, wasn’t the only one who came away wide-eyed after a 90-minute tour of Southern California Edison’s (SCE) San Onofre nuclear plant.

Many of the 50 visitors who went on recent walking tours expressed surprise about not only the size of the 84-acre plant and its iconic cement domes, but also about the process of generating electricity with nuclear power and storing the used nuclear fuel safely on site.

Although the San Onofre plant began operating more than 40 years ago, SCE did not routinely provide public plant tours. Last fall, with the nuclear generators shut down and the plant starting the 20-year process of decommissioning, SCE began hosting twice-monthly tours on-site for the public.

Ron Pontes, San Onofre’s manager of decommissioning, led Krumboltz’s tour. He provided an overview of the plant’s history, dating back to the construction of Unit 1 in the mid-1960s. He noted that the two remaining units, which were retired in 2013, once generated 2,200 megawatts of electricity for Southern California — enough to meet the needs of 1.4 million homes and businesses.

Standing on a hill above the facility, Pontes pointed out the concrete-clad Independent Spent Fuel Storage Installation and explained the process of removing and safely storing used nuclear fuel first in enclosed underwater spent fuel pools and later in dry cask storage.

The group then moved to one of four viewing areas where easels were mounted with blow-up, poster-sized photos of the plant and its inner workings. About halfway through the tour, Pontes stopped the group near the switchyard.

The tour ended on the flat rooftop of the administration building, where visitors get an up-close view of the domed Unit 2 containment building. Although tour participants do not go inside the plant buildings, they learn about how the facility was operated and the current decommissioning process during a 1.5-mile walk around the facility.

David Faultersack, a retiree from San Juan Capistrano, could not contain his glee at the sight.

“This is exactly like the model I had when I was a kid in the 1960s and nuclear power was the in thing,” he said.

As the group headed back up the hill to the parking lot, they were asked to give wide berth to one of the low-lying buildings they were passing to keep from disturbing a seagull that was tending to two fuzzy football-sized babies in a nest.

Twelve-year-old MacKenzie Moore of Lake Forest, who went on the tour with her mother, Julie, said the baby seagulls were the highlight for her.

When the tour ended, Krumboltz was still talking about how surprised she was at the plant and how much she had learned.

“I would come again,” she said.