Question: Repentance Tower was built in 1565, and served as a watchtower for what tower house that is located by the River Annan?
Context: Annan Castle, was a castle that was located on the banks of the River Annan, in Annan, Scotland. Xlejli Tower (formerly spelt Shilejli Tower, Maltese: "Torri tax-Xlejli "or" Torri Xulliela" ), also known as Bettina Tower, is a tower in Gudja, Malta.  It was probably built as a watchtower since it has views over a large area of land.  The age of the tower is not known, and it could date back to the Roman or medieval periods, or possibly a later reconstruction.  The tower is now located in the grounds of Palazzo Dorell, and it is closed to the public. Greenknowe Tower is a 16th-century tower house, located just west of the village of Gordon, in the Scottish Borders.  Although a roofless ruin, the stonework of the tower is well preserved, and represents a fine example of a later tower house, built more as a residence rather than as a place of defence.  The building is located at [ NT639428] , beside the A6105 road.  It is a Scheduled Ancient Monument, and is in the care of Historic Scotland. Hoddom Castle is a large tower house in Dumfries and Galloway, south Scotland.  It is located by the River Annan, 4 km south-west of Ecclefechan and the same distance north-west of Brydekirk in the parish of Cummertrees.  The castle is protected as a category A listed building. Repentance Tower is a 16th-century tower house situated near Annan, Dumfries and Galloway.  Built in 1565 by John Maxwell, it served as a watchtower for Hoddom Castle.  The tower takes its name from an inscription above the door. Orchardton Tower, is a ruined tower house in Kirkcudbrightshire, Dumfries and Galloway, south west Scotland.  It is located 4 miles (6.1km) south of Dalbeattie, and 1 mile (1.7km) south of Palnackie, in Buittle parish.  It is remarkable as the only cylindrical tower house in Scotland.  Orchardton Tower is in the care of Historic Scotland, and is a Category A listed building,and a Scheduled Ancient Monument. A tower castle is a small castle that mainly consists of a fortified tower or a tower-like structure that is built on natural ground.  It is thus different from the motte-and-bailey castle, which it may resemble, but whose main defensive structure is built on a "motte" or artificial hill.  The tower castle is occasionally also described as a tower house castle or a tower house. Mahee Castle, also known as Nendrum Castle, is a small ruined tower house near Nendrum Monastery on Mahee Island in Strangford Lough, County Down, Northern Ireland.  It was built in 1570 by Captain Thomas Browne.  It was abandoned by the early 17th century, and fell into disrepair.  In 1923, H.C. Lawlor and the Belfast Natural History and Philosophical Society partly renovated the tower house to avoid further erosion and built a buttress wall to support the northwest corner of the tower. The Birgu Clock Tower (Maltese: "It-Torri tal-Arloġġ tal-Birgu" ), also called the "Vittoriosa Clock Tower" and originally the Civic Clock Tower, was a clock tower in Birgu, Malta.  It was located in Victory Square, the city's main square, and it was a prominent landmark in Birgu and the rest of the Three Cities.  The tower was probably built in the Middle Ages, although some sources state that it was constructed in 1549.  It served as a watchtower since it had views over the Grand Harbour and the surrounding countryside, and it saw use during the Great Siege of Malta in 1565.  A clock was installed in the tower in the 17th century. HMS "Annan" was a River-class frigate built for the Royal Navy but was transferred to the Royal Canadian Navy before commissioning.  She served with the Royal Canadian Navy during the Second World War and saw action primarily as a convoy escort in the Battle of the Atlantic.  She was returned to United Kingdom following the war and quickly sold to Denmark, who renamed the vessel "Niels Ebbesen".  She was primarily used as a training vessel until 1963 when she was broken up in Odense.  She was named for the River Annan in Scotland in UK and Canadian service and Niels Ebbesen in Danish service.
Answer: Hoddom Castle