Gary Cypres of Brentwood owns the original, 1889 hand-written letter admitting the Dodgers baseball team to the National League.

But that’s just the beginning of his collection.

There’s the 1934 tour Babe Ruth took to Japan. Cypres has got the Bambino’s jersey from that trip.

Also in his possession: one of the famous and rare Honus Wagner trading cards, the 1941 Heisman Trophy of the University of Minnesota’s Bruce “Boo” Smith and thousands more pieces of sports memorabilia from the world of baseball and beyond.

In short, the 62-year-old entrepreneur has one of the best collections of American sports memorabilia amassed by an individual. “You could not go out and assemble what he’s done if you had a blank checkbook,” says David Hunt, president of Hunt Auctions. “The materials don’t exist.”

And they’ve sat relatively unnoticed in a nondescript warehouse at the corner of Washington and Main streets in downtown Los Angeles – at least for now.

While Cypres has offered private tours of the collection, next April, if all goes according to plan, the Cypres Sports Museum will open the treasure trove to the public. And for an expected $15 entrance fee, sports buffs will walk into what resembles the biggest, coolest sports bar they’ve ever been in, sans the booze of course.

The experience is a mind-expanding stroll through American sports history, from the 19th Century era of fingerless mitts and nickel admission tickets (such as a turn-of-the-century peanut roasting machine) to the present-day steroid era and $100 million contracts. There are more than 10,000 items in all.

Vintage movie posters, such as “The Story of Seabiscuit” starring Shirley Temple, adorn the walls of one room, while another holds thousands of trading cards, dating all the way back to 1887. Game uniforms of legends from Wilt Chamberlain to Sandy Koufax hang overhead, while separate spaces feature vintage prints by photographer Charles Conlon.

There are also antique bicycles, autographed bats, early advertising posters, and Carl Tolpo’s remarkable folk-art paintings of baseball’s greatest stars. (Cypres keeps his T206 Honus Wagner tobacco card – one of the most famous trading cards ever issued – in a safe.)

While he won’t say how much he’s spent, Cypres estimates it would take “north of $30 million” for someone to buy the entire cache, if you include the property and the building.

“To try and get an economic return on this is impossible,” Cypres said, “but I thought this would be a pretty neat thing for the city to have.”

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Born and raised in the Bronx – or, as he likes to put it, “in the shadows of Yankee Stadium” – Cypres played basketball and studied business at Hofstra University on Long Island. But while he always loved sports, business became his vocation.