Southsea Castle was part of a series of fortifications built by Henry VIII to help defend England from invasion. Constructed in 1544, it guards the entrance to Portsmouth Harbour; Mary Rose sank right in front of the castle in 1545. The castle was captured just once in its history, by Parliamentary forces during the Civil War, its fortifications were strengthened in the 19th century and it continued in use up to the Second World War. Since then, it fell into disrepair but has been extensively refurbished. It's not huge, there is a small but interesting exhibition, defensive tunnels and great views over the Solent to the Isle of Wight from its battlements. At time of writing (2017), there is a cafe and a microbrewery in the courtyard and the castle is closed in winter months. Essential to check the website before visiting.