Harry's Walls

Harry's Walls are the remains of an unfinished artillery fort, started in 1551 by the government of Edward VI to defend the island of St Mary's in the Isles of Scilly. Constructed to defend the harbour of Hugh Town from possible French attack, the fortification incorporated Italianate-style bastions with protective orillons and would have been the most advanced design in the kingdom at the time. It was not completed, probably due to a shortage of funds and the passing of the invasion threat, and only the south-west side remains. In the 21st century, Harry's Walls are managed by English Heritage and open to visitors.

Source: Wikipedia