I saw some ideas to add generated treasures, but as most things created by players, they should also be able to bury chest in the ground.
Why?
1. Another level of security when claims and walls are fallen. For example you can hide master keys and not use extra person
2. Some bored players may create quests for beginners and others. Pirate maps are waiting for you!
How it should work?
New option in adventure menu to bury. Dig on exact tile and exact depth (arguable) and you automatically lift chest.