The Field Museum’s main galleries are plenty wondrous. But some overlooked marvels of the deep live below the encyclopedic exhibition halls, where most visitors might not think to look.

Behind a gift shop and flanked by vending machines and a smattering of pastel-colored lunch tables, a herd of narwhals is suspended in a perpetual dive.

The average visitor is unlikely to ever come closer to one of these whales. They live in Arctic waters, where they’re known to plunge to depths of up to 1,500 feet, and attempts to keep them alive in captivity have brought one flop after another.

Narwhals look otherworldly; fittingly, they’re sometimes called the unicorns of the deep. Like that fantastical beast, they appear to have a tusk protruding from their heads—but in this case the “horn” is very real, and it’s actually a type of tooth.

The ones in the Field Museum were collected roughly a century ago, on a northbound journey aboard a boat that became lodged in ice. Today, they’re a wondrous reminder of the mystery and majesty of the deep—and you have to stray from the museum’s beaten path to find them.

Update as of  September 2019: The interior has been redecorated and the narwhals are no longer viewable. 

Update as of January 2020: The narwhals are once again viewable.