ROTTERDAM—Dutch art and design museum Boijmans Van Beuningen on Friday opened a stunning mirrored warehouse called the “Depot” to display the great bulk of its collection normally kept in underground storage, hidden from public view. While most museums only have the space to show a small part of their overall collection, the Rotterdam art museum has now unveiled 151,000 works of art for the public in an airy, multi-storied, steel and glass building. Boijmans director Sjarrel Ex told Reuters that art museums typically show just the tip of the iceberg of their collection, meaning a staggering 93 percent of works are never on display. “There is a moment where the things you [cannot] look at sink into oblivion,” Ex said, adding the new building can accommodate over 60,000 visitors a year on guided tours or following a set walking route. The depot, which features figurative Dutch art from the early …