a treasure chest  

In Fungal Forest: Spawns following the "Fungal Corruption" raid event (see the link for event information).

In the Plane of Innovation: Spawns as you complete the Veil of Alaris pre-launch mission "Engine Trouble" (see this quest entry for information).

In Windsong Sanctuary: Spawns as you complete the group mission "The Sound of Silence" (see this quest entry for details).

In Zeixshi-Kar's Awakening: Spawns as you complete the group mission "Confronting Your Fears" (see this quest entry for details).

In Valley of King Xorbb: Part of the group mission "Find the Gems... Or Die!" (see this quest entry for details). Note: an ornate chest is the loot chest for this mission.

In the Plane of Mischief: Part of the group mission "Piestro's Day Off" (see this quest entry for details).

In Timorous Deep: This is a bonus chest in the anniversary mission "Pirates of Timorous Deep" (see this quest entry for details).