Treasure chests, also known as chests or item chests in The Lost Frontier, are containers in The Precursor Legacy and The Lost Frontier, serving a different purpose in each game. In The Precursor Legacy, the wooden chests are similar to the barrel, containing droplets of either small healing green ecos, a large green eco, and sometimes blue eco or yellow eco. They are rather small, each side consisting of two or three wooden planks bound by metal plating, with no other decoration than two metal handles on either side.
In The Lost Frontier, the chests contained either armor or Gunstaff upgrades, the brown chests being the former and the blue the latter (although there is also one special green chest, which contains the last armor set, Dark Sage's Mail). They would remain closed and surrounded by a golden aura until Jak approached and opened one with , at which point it would open and the aura would disappear, exposing the chest's contents as Jak reached into it.
For the armor, a sound of Jak fitting in the armor will sound as the screen goes black before panning towards Jak, showing him clad in his new armor. For the gunstaff upgrades, the gunstaff will appear on Jak's back (the only time this occurs in-game), switching to the respective mod, before Jak grabs the mod, takes the gunstaff off his back, and attaches the mod. Afterwards, the chest can still be seen upon returning to the area at any point in the game, and unlike those in The Precursor Legacy were indestructible.
Also unlike those in The Precursor Legacy, the chests appeared to be made entirely of metal, with either copper or bronze decorations and a keylock on the front.