Detroit’s Guardian Building is pretty remarkable from the sidewalk: The bricks are painted a light tangerine, and colorful details are clustered up high, to arrest the attention of motorists zipping by far below. It stands 40 stories tall, and two stone figures stand sentry by the doors. The real marvel, though, isn’t visible from the the outside.

Indoors, everything from the elevator banks to the soaring vault ceiling is awash in a riot of color. The geometric blue, green, and ochre mosaics—many made with tiles crafted at Pewabic, a local pottery firm—borrow from Aztec and American Indian patterns. A massive mural of the state of Michigan, ribboned with gilded details and homages to the state’s natural resources, looms on the far wall. All this, just upstairs from an unassuming snack shop and county commissioners’ offices.

The building opened in 1929 to house the Union Trust Company in an era when the city was pushing to establish a solid financial district. The structure towered over much of the rest of the skyline and earned the nickname the “Cathedral of Finance,” a nod to its kindredness to the Woolworth Building in New York.

Brick, teracotta, marble, and metal details—not to mention an opulent Tiffany clock—add up to something wondrously dizzying. Putting it all together was no small feat, and a tile in the lobby commemorates the dozens of artisans who worked to make it all come together.

The building changed hands and tenants a number of times over the years but ultimately survived a slew of economic tumbles and the city’s changing industrial landscape. Today, you might see locals charging their phones or taking a lunch break in the former banking hall—one of the city’s grandest public spaces.