You see a treasure chest.
Location
Amazon Camp Treasure Room, Bregar Treasure Room, Darashia Catacombs Treasure Room, Ferumbras Citadel Treasure Room, Kazordoon Treasure Room, Nargor Treasure Room, Pits of Inferno Treasure Room, Yalahar Treasure Room and some banks. It can also be seen in The Flaming Orchid's room in the Asura Palace and behind Bars near Palimuth.
Notes
Most of them are unreachable. There is also an overfilled variant:
It has the same name but looks different from the Blue Treasure Chest