Closed chests along with the castle remains in the background will not disappear if its area is deforested.
Not to be confused with the Tax chest.
There is a coin chest in the center of ruins. If the Monarch is not running at full speed past it, the chest will open up and spill out twelve coins (eight in Kingdom: Classic). After collecting the riches, the chest disappears permanently.
Coin chests are good for getting money quickly and very valuable on later islands.
Kingdom: Classic – The chest will open even if the Monarch passes by them galloping.
Occasionally in the ruins, instead of a coin chest, there is a gem chest. If the Monarch passes in front of it walking (not galloping), the chest will open up and spill out two to three gems. After a few seconds, the open chest disappears permanently.
A gem chest can though be ignored by passing in front of it galloping.
A closed gem chest will never disappear, even if the forest around it is fully removed, if the Monarch travels to other lands, or if the Crown is taken. The chest will remain on the field until it is triggered to open.
TIP: It may be wise to not immediately collect from a gem chest, as gems lower the capacity of the pouch for coins.