Chests are the most common type of container which can be opened for potential treasure. They may be opened by any player by clicking on them like any other object. They may contain items and/or gold, but sometimes don't contain anything. Their contents depend on the Area Level of the area in which the chest is present.
There are many different kinds of chests, from simple boxes to ornately decorated varieties, but they all function about the same.
Some chests are spawned as locked chests. They can be only opened with a key. Each time you open a locked chest, one key is deducted from your inventory. Assassins are expert lock-pickers and do not require keys to open locked chests.
Some chests may also contain Traps.
Some chests, usually at the lowest levels of dungeons, can spawn as golden (or sparkling) chests. These chests get a bonus to their item drop by boosting their Area Level. They often drop only magic items, as well as a lot of gold. Some are also the source of specific Quest Items.