In September of 2010, we took a look inside the U.S. Mint at 155 Hermann Street to learn about the operations and history of this mysterious building. This morning, for the Mint's 75th birthday, we returned.

San Francisco's "New" Mint was officially dedicated on May 15th, 1937, and to commemorate the occasion, today the Mint allowed media and political figures inside for a special ceremony and tour of the facility. We were allowed much greater access than during our visit in 2010, and were able to take photos of pretty much anything we wanted. So, here are a few of our favorites from the day's festivities.

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Here's what the Mint does best: produce coins. There's a press room, for... pressing. In the materials room, the coins get their shiny luster. In another room, employees work on polishing the coin dies. This man was using a brush with a horse-hair tip. There are several finishing/frosting options employed, depending on the coin. Then the coins get packed into cases and cardboard sets via conveyor belt. (This used to be done by hand, up until around 1999.) Two giant yellow robots keep everything organized. Workers receive an annual binder training them about that year's coins and explaining which defects to watch for. The finished products are stacked and sent out to another facility for shipping to customers... ...except for the rejects, that is. We saw lots and lots and lots of coins today. Here are some silver dollar proofs. Here's a finished 5-piece proof set, available online and via phone. This bin contains upwards of $1 million worth of quarters, we were told. Some $1 dollar coin proofs... ..and more silver dollars. These are blanks, which will be turned into quarters. The San Francisco Mint hasn't made quarters for circulation since 1954. However, this year, they've resumed manufacturing the coins. The reason? The quarters, featuring San Francisco's "S" mark, can command a significant premium from collectors. It's all about money, you see. More beautiful coinage. We had the pleasure of meeting a number of fantastic people who work at the Mint, and some fellow attendees of the day's event. Our guide for the day, Loretta Dickerson (right): An employee manning the lobby's display case: Police performing a color ceremony before the morning's speeches began. The Mint's historical guru Michael Levin. A representative (left) for Assembly member Fiona Ma presents a proclamation to a rep for the union representing the Mint's 300 employees. An employee examines coin sets coming off the assembly line. Two workers show the first coins from the 2012 proof set, just struck during the ceremony. Many banners and displays around the building recognized the 75th anniversary. Safety is obviously a huge priority at the Mint, especially in the production areas. Doesn't matter how old we get: lasers will always be cool. Mayor Lee's office issued a proclamation declaring May 15th, 2012 "U.S. Mint Day." The mayor was invited, but did not attend today's ceremony. Historian Michael Levin cited a precedent, noting that at the building's dedication in 1937, both the mayor and governor were no-shows. Inside the amazing lobby. A rose compass on the floor points South to 350 Duboce, the building's former entrance. A close-up of the floor's compass, featuring a serpentine center. A close-up of the door. A seal and plaque on the wall celebrate the building's construction. A functioning art deco elevator maintains its original design and details from 1937. A pair of eagle statues flanking the lobby stairwell. The stairwell's wall features a series of galvanos, or oversized coin models. A reverse view of the stairwell from the mezzanine. Finally, here are a couple of secret spaces we glimpsed during out tour. A cafeteria / break room: And the Mint's courtyard. After more than two hours inside the Mint, the ceremony and tour concluded and it was time for us to go. Another great day at the Mint. Here's hoping we won't have to wait 25 years for the next one!

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That's it for our second look inside the Mint. But as a reward for your readership, we've got a special treat. One lucky Haighteration reader will win a 2012 Clad Quarter Proof Set, manufactured right here at the San Francisco Mint! To win this set of five shiny beauties, all you have to do is leave a comment on our Facebook post for this story, telling us something you can buy in the Lower Haight for five quarters. Leave your comment by this Thursday, May 17th, at 5pm, and we'll pick a winner Thursday night.

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Thanks to everyone at the Mint for inviting us today and letting us peek into their world yet again, albeit briefly. It was a treat.