Half a mile from the town centre of Falmouth, Cornwall, lies the imposing round tower of Pendennis Castle. Located at the entrance to the River Fal, Pendennis, and its sister castle, St. Mawes, were constructed to protect the waters called the Carrick Roads. The castle sits on a hill with an extensive view of the surrounding area. It is sometimes called a gun fort due to the abundant artillery and other military elements.

Since it was built purely for defensive purposes, the castle has none of the elaborate architectural elements found at other sites. It has a simple three-storey round tower, attached barracks and storehouses, and a gate, enclosed by a lower curtain wall. The basement of the tower contains the kitchen, with two gun decks above. Each gun deck held seven cannons. On the roof of the tower is a look-out post with its own fireplace for heat. The Governor's rooms, including a parlour and dining room, are located in the entrance block, reached by a drawbridge over a dry moat. The Governor's building does have a few decorations such as stone gargoyles.