This skill is gained at level 50 when you evolve into a Buccaneer. This skill allows you to use certain forms of explosive to blow open cracks in the ground, these cracks are located on each island in the map (yes this means you have to control some islands to access all of the treasure seeking content).
Clicking on the crack on the ground will cause you to use any explosives in your inventory to blow open the crack and descend into a series of tunnels below the realm.
These tunnels are extensive and cover 1000 levels of monster content, with sub-bosses in various parts so you may not be able to complete the entire dungeon in one go, nor are you meant to.
It is advisable to take 10 - 20 parts of explosive with you so that you do not come to a part where you can not continue.
The sub-bosses all drop a part of a treasure puzzle, when you combine all 50 parts of the puzzle you can get some nifty prizes.