The 500-Square-Inch Triangle of Pure Spite Hidden in a West Village Sidewalk

At Seventh Avenue and Christopher Street, a mosaic triangle smaller than a doormat has been insulting New York City for over a century. Meet the Hess Triangle — the city’s tiniest, pettiest landmark.
The Glittering Lampposts Everyone Walks Past: How to Find Jim Power’s Mosaic Trail in the East Village

For nearly 40 years, one Vietnam veteran has been encrusting East Village lampposts with broken china, marbles, and mirror shards — for free. Meet the Mosaic Man and walk his trail from Astor Place to Tompkins Square Park.
There Is a Museum Across the Street From Grand Central Devoted Entirely to Dogs — and You Can Bring Yours on Fridays

Inside a glass storefront across from Grand Central sits one of the world’s largest collections of dog art, an interactive arcade where you can sketch your own breed, and a Friday policy that lets you bring your actual dog inside.
The Strangest Apartment in SoHo Is Filled with 280,000 Pounds of Dirt — and You Can Visit It This Sunday for Free

At 141 Wooster Street, behind an ordinary SoHo doorway, Walter De Maria’s The New York Earth Room has been sitting since 1977: a 3,600 square foot loft filled with 280,000 pounds of black soil, free to visit, Wednesday through Sunday. Here is what it feels like inside, why it works, and the exact afternoon hour you should show up.
The $5 Museum Above a Brooklyn Freak Show: Why the Coney Island Museum Is NYC’s Most Joyful Five Dollars

Up a flight of stairs on Surf Avenue, above the last permanent ten-in-one freak show in America, sits a $5 museum packed with bumper cars, Fun House mirrors, and the saved-from-the-wrecking-ball memory of the place that invented American fun.
The Free Manhattan Museum Hidden Behind a Stone Lion Gate: Why the Hispanic Society Is the City’s Best-Kept Sunday Secret

Behind iron gates on a forgotten Beaux-Arts plaza in Washington Heights, a free museum holds Goyas, El Grecos, and Sorolla’s monumental “Vision of Spain” — and almost no one in NYC has ever walked inside.
The Smallest Piece of Private Property in New York City Has Been Quietly Scolding the City Since 1922

A 500-square-inch mosaic, embedded in a West Village sidewalk for over a hundred years, is technically private property. The story behind the Hess Triangle – the most New York real estate dispute ever recorded.
The Free Russian Museum Hidden in an Upper West Side Brownstone Where the Himalayas Live: Inside the Nicholas Roerich Museum

On a quiet block of West 107th Street, behind an unmarked brownstone door, three floors of mountainscapes glow purple and gold above the Upper West Side. The Nicholas Roerich Museum has been free since 1949 — and almost no one in New York has ever set foot inside it.
NYC Has the Only Math Museum in North America — And It Just Got a Wild New Home in Chelsea

You can ride a tricycle with square wheels and have it roll perfectly smoothly. You can watch a giant laser slice through geometric shapes in mid-air. You can sit inside a mirrored tunnel that seems to stretch to infinity, or trace the invisible paths that a bouncing billiard ball would take through an endless table. […]
The NoHo Townhouse Frozen in 1865: Inside the Merchant’s House Museum, Manhattan’s Last Intact 19th-Century Home

On a Sunday afternoon in NoHo, you can walk into a Greek Revival rowhouse where the Tredwell family’s furniture, china, and ghost stories have been sitting undisturbed since the Civil War.