The watchtower on the opposite slope to the castle is also probably 16th-century, or possibly late-15th-century and is shown in a state of completion in a view of the castle dated 1740. It decayed thereafter, was restored in the late-19th century, but is again derelict in the early 21st century. It was almost certainly intended as a seaward look-out.
As of my return visit in 2019 the tower has been sealed with no access possible.