The Sea Cages are a collection of rusting iron cages, each just big enough to hold a single humanoid. They are bolted in to the foundations of the The Redoubt in the town of Skull River Bay.
The cages are above water during low tide but during high tide they are completely submerged . Prisoners to be executed are locked in the cages when the tide is low and slowly drown as it rises.
The cages are close to town so the screams of the unfortunate victims are easily heard by the town residents.
The cages are impossible to escape from, from inside, and their proximity to The Bastion means guards are constantly watching them , making rescue extremely difficult.