“Excuse me ma’am, which floor are you going to?”

No sooner had I entered the Shanghai Tower than I was whisked aside by two security guards and asked the nature of my visit.

The security guards likely mistook me for an overeager tourist. Fair enough — as I spoke with them, I could see a tour group filing into the building behind me. They jostled and tittered about like any tour group but suddenly fell silent when their guide announced, “Up next, we’ll be visiting the Shanghai Tower’s underground vault.”

Stories about the safe-deposit boxes in “Vault 1,” located 25 meters below ground level, have gone viral in recent weeks. The Baoku Treasury — owned by Baoku China — is the largest underground vault in China, reputed to be even more secure than banks. The company motto is “No one but you will be able to open your safe-deposit box.”

Of course, this level of security doesn’t come cheap. The smallest compartment, measuring 127 by 286 by 600 millimeters, costs 68,888 yuan (about $10,300) for 15 years.

I met the owner of one of these safe-deposit boxes, Zhou Ming, in the Baoku Art Center’s VIP lounge on the skyscraper’s 37th floor.

Everyone has something precious they want to keep safe. Zhou’s two favorite toys as a child were a small cast-iron frog and a toy handgun. The toys were lost at some point in his youth, but he told me that he would be deeply moved if his parents were somehow able to produce them.

Zhou has a 3-year-old daughter. In his safe-deposit box he keeps a lock of hair from when she was born, a mold of her tiny foot, and a drawing he did with her when she was in kindergarten.

Besides keepsakes, Zhou also uses his safe-deposit box to store valuable materials, including bars of gold. His plan is to wait until his daughter is engaged before giving her the keys and telling her, “This is your dowry; take it.”

But Zhou also has a plan B: “If my daughter mistreats me and my wife when she’s older, I’ll use the gold to take her mother on a trip around the world.”

The vault’s security procedures are thorough. First, visitors must have their vault-issued ID cards verified by the guards. Then they have their palms scanned before being accompanied into the vault by an employee who holds a service key. To unlock the safe-deposit box, both the employee and the visitor must insert their keys into the panel and turn them at the exact same moment.

This level of security has led to speculation about the kinds of personal items that people would want to guard so tightly.

A host from Shanghai Television said he uses his box to store video recordings from his early days in the industry. The vault is specifically designed to be a safe storage space for historical relics: As long as he can find a working VCR in the future, his videotapes will still be watchable.

People have used the boxes to store everything from cellphones to love letters. There are some who safeguard jewelry; others keep the deeds to their mistresses’ homes locked away where no one will ever find them.

Of the 18,000 safe-deposit boxes in Vault 1, 20 to 30 percent are reserved for use by businesses in Shanghai’s financial district, which use them for secure data storage. Several thousand more are reserved by the government, leaving approximately 10,000 boxes available for personal use. Six thousand of these have already been sold.

In addition to the Baoku Treasury, there are around 20,000 safe-deposit boxes scattered around the city’s financial district. However, only 20 percent of these are available to the public.

The rest are reserved for bank employees and VIPs. For this reason, private safe-deposit boxes have historically been a lucrative investment, with almost all of the ones in the financial district being snatched up prior to the opening of the Baoku Treasury.

The idea for the vault came to the company’s founder, Liu Feiguo, while he was lobbying to open an art museum in the Shanghai Tower. He realized that the high revenues from the Baoku Treasury could fund the museum’s daily operations.

Baoku Treasury clients are given a 15-year membership pass to the Shanghai Guanfu Museum and the Baoku Art Center, allowing free access to exhibits and events. Most of the proceeds from deposit box sales are reinvested in the museum.

Baoku China has already announced plans to expand and build community vaults. According to Zhou, “Community vaults are actually cheaper to build than high-end swimming pools.”

In the end, whether people are looking for a place to store their wealth, hide their secrets, or keep their investments secure, the market for third-party safe-deposit boxes is steadily growing. I suppose that to some people, a small metal drawer brings a great deal of comfort.

(A Chinese version of this article first appeared on China30s.)

(Header image: Moment Open/VCG)