SACRAMENTO — If you’ve ever wondered how Amazon can send you that book/detergent/Halloween costume so quickly, you now can see for yourself.

Nearly two dozen warehouses — Amazon calls them fulfillment centers — belonging to one of the world’s largest retailers are offering public tours twice a day every weekday. We recently visited the 855,000-square-foot one in Sacramento, named after the airport that’s a few miles away: SMF1.

Why has Amazon expanded its public tours from a couple of times a month at a few facilities to everyday tours at 23 warehouses in the United States and Canada?

Our tour guide, Amber Lord, told our group of about 30 people — including four journalists — that the company was simply fulfilling curious customers’ wishes.

It’s a little more complicated than that.

“Amazon expanded our tours program because we are proud of the safe and positive work environments we offer associates and want to share it with customers and the general public,” Amazon spokeswoman Shevaun Brown told this publication. “A lot of stories about working in our FCs are inaccurate and misguided, so we encourage anyone to see for themselves.”

Working conditions at the company’s warehouses have made headlines for years, so much so that Amazon has deployed word warriors on Twitter — known as “FC ambassadors” — to fight its PR battles. There have been many strikes at Amazon warehouses in Europe, including walkouts in a few European cities during Prime Day last month. Workers in Minnesota also went on strike during Prime Day, the latest of U.S.-based employees who have taken action this year. Amazon workers reportedly are demanding better wages and working conditions and are seeking to unionize.

What we saw in Sacramento: Workers stowed, picked and packed products for delivery at the four-floor warehouse, which stocks more than 4 million different types of items. About 2,500 employees there have 10-hour shifts four times a week, with two 15-minute breaks and a 30-minute lunch each day.

In the areas we were allowed to see, most employees worked independently of one another. The guy who scanned and stowed items into towers of shelves, Jay, stopped for just a moment and nodded as the tour guide asked him how he was doing. The shelves were being rolled around the warehouse floors by a couple thousand orange robots that resemble big Roombas, except they’re rectangular.

Those robot-transported towers of shelves then made their way to pickers such as Alicia. At her station, she watched a computer monitor that told her which items to pick and put into big yellow bins. She then sent those bins to a conveyor belt and onto the next process.

The packers were our next stop. Kevin picked items out of the bins that people such as Alicia had filled, then placed them into boxes. He then sealed the boxes with tape and sent them on a conveyor belt that scanned them and placed shipping labels on them. Final stop in the warehouse: pallets that were loaded onto trucks.

Someone taking the tour, which included families with kids on their final day of summer vacation, asked how much the workers make.

“We’re a leader in providing a livable wage,” said Lord, the tour guide. Workers at the Sacramento warehouse make from $15 an hour — which starting last year became the minimum wage for all of the company’s U.S. employees after political pressure from lawmakers such as Sen. Bernie Sanders, I-Vermont — to $18.85 an hour.

She also touted Amazon Career Choice, which is available to full- and part-time employees who have worked at the warehouse for at least a year. Amazon pays up to 95% of tuition and fees toward a certificate or diploma for careers in transportation, health care, mechanical or skilled trades, and IT and computer science. The company says 18,000 U.S. employees have taken advantage of the program since its inception in 2012.

But when asked what the turnover rate is at the facility, Lord said she didn’t have those numbers. Brown, the spokeswoman, said the company doesn’t share those figures.

The workers we saw on our tour seemed comfortable enough. The temperature was about 90 degrees outside, but inside it was pleasant. However, they rarely stopped working during the 45 minutes we were there. When Jay was stowing items, he was being timed on how long it took him to put each one on the shelf.

Some workers have complained about being held to impossible standards. They have written about their experiences in books, blogs and job sites. They complain of physically demanding work that is hard to do long term. Other warehouse worker complaints include having to stand during their whole shifts and not being able to use the restrooms unless they’re on their breaks.

A couple of current and former warehouse workers who asked to remain anonymous told this publication that they had no problem with their working conditions.

A retired U.S. Postal Service employee said working at Amazon’s Vacaville facility — where he had four-hour night shifts loading packages onto pallets — was easier than the post office. But that facility has about 250 workers, about a tenth of the number of workers at the big Sacramento facility.

A current employee at an Amazon Prime Now facility in Sacramento said he likes being assigned to a different task each time he shows up for his mostly five-hour shifts a few times a week. He said the workers there also are timed on everything they do, but as he understands it he and others are under less pressure than workers at the bigger warehouses. They don’t have robots there, so they have to walk around the warehouse to pick or stow items.

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Proposal emerges for Amazon-linked San Jose site He also mentioned that some of his colleagues who came from the bigger warehouse in Tracy said they viewed working at the smaller Prime Now facility as an improvement.

“They did say the culture here was a lot better than the big warehouse,” he said.

The public tour, which can be booked online by going to the about page on Amazon’s website, at SMF1 seemed to do what it was meant to do. Those who attended were impressed.

“I’ve been curious about the process and the robots,” said Susan Francisco, of Sacramento, who took the tour with a friend. “(Amazon) is so reliable.”