Gravedigger is a random event in RuneScape in which the player is teleported to a small enclosed cemetery with five open gravesites, each containing a coffin and marked headstones. The player has the option to deposit anything in their inventory they wish to directly into their bank account; however they do not have the ability to retrieve any other item or get back the ones they deposited - so be careful.
The objective in this event is to match each coffin up with its respective headstones as requested by a gravedigger named Leo. You will read each headstone and by either using memory, writing or a text file you must remember what player roll is depicted on each headstone as a photograph of an item related to a skill.
By inspecting each coffin, you also get a series of bones and items within the coffin which will allow you to see which coffin is a farmer, miner, woodcutter, etc. Place these coffins into their corresponding graves in front of the headstones, and then talk to Leo to receive a reward and to be teleported back to your previous location.
As there is a bank deposit in this minigame it's worth participating already just to be able to bank the loot gained during the activity you were doing before if you were engaged in an activity such as killing monsters for loot or training gathering skills.