While the Central Stacks have been a part of the New York Public Library for over 100 years, the Milstein Stacks were only integrated into the plan in the 1980s, when the collections spread underground.

Recently we took a look at Milstein II, the new soon-to-be active storage space set to open in 2016, but above that is Milstein I, which began operating in 1999. These are both located in what can be considered the basement and sub-basement of Bryant Park, 17-feet and 27-feet below the lawn, and are each treasure chests holding millions of items—from historical to modern gems. Where else can you find the latest edition of Cemetery Dance magazine? Here's a look inside:

(Video by Jessica Leibowitz/Gothamist)

Still have questions? Here's our FAQ on these beloved vaults.

What's in there? Inside these Milstein I rooms you'll find books published in the last 25 years, as well as historical items.

And? According to the NYPL's Denise Hibay, there are also "special vaults for special collection material, for manuscripts, archives, rare books, photographs, and maps. The kind of materials that are shelved in very special ways, not on shelves for books."

Is this space all filled up? No, Hibay explained, "we have room for growth here. We shelve things by size... because of that, and because we’re a closed-stack library, meaning that only the staff come to retrieve the books, we’ve been able to shelve things by size. So you can find a novel next to the writings of John F. Kennedy next to a book about cookery or about German literature. So it’s quite a mixed collection in that sense."

(Photo by Amy Finkel/Gothamist)

What about the microfilm? The collection has well over 350,000 reels of microfilm, which include newspapers, and the humanities and social sciences. So if you want to see a 1970s edition of Ms. magazine, or Rolling Stone when it was a folded newspaper, you will be able to find it here. There are 350,000 microfilm reels, and approximately 6,000 print publications on hand.

What about more current periodicals? Those are stored in the stacks. Karen Gisonny, the Library's Curator of Periodicals, notes that the collection is one of a kind—"It covers many languages, it’s global in scope, the subjects are humanities, social sciences, and a wide, wide range of popular cultural general interest magazines."

The periodicals are stored alphabetically. (Photo by Amy Finkel/Gothamist)

Like what? "Everything from culinary and fashion, sports, games, collectibles. Things that are not widely held in many public institutions," Gisonny explained. "We have a huge range of collectible magazines... like Doorknob Collector, Teddybear Review, Check the Oil, which is for people who collect gas tanks and everything having to do with oil and gas from the 1950s."

Got anything for a funeral director or someone in the sex industry down there? "We have industry magazines, so professional journals like American Funeral Director, and something called Spread, which is written for people that work in the sex industry."