Every neighboring castle contains a special red treasure chest. The contents of the chest vary depending on your neighbor's level. To get inside the castle, you must destroy one of its walls with a bomb or powder charge. Be careful: the sound of the explosion may attract unexpected guests. To open the chest, you need a key that is held by the castle's owner.
Neighboring Exiles periodically travel around the Plaguelands and can easily be distinguished from other Exiles from their nickname and the color of their health meter. Until a castle location is refreshed, you may encounter your neighbor and fight them to acquire the key to the special chest.