Castelo de Sao Joao do Arade, also known as the Arade Castle, is a medieval fortress located in the city of Portimao in the Algarve region of southern Portugal. The castle was built in the 15th century as part of a system of fortifications along the Algarve coast, designed to protect the region from attacks by pirates and other invaders.

The castle was originally constructed by King Joao II of Portugal and was later renovated in the 17th century by King Joao IV. It is built on a hill overlooking the Arade River and was strategically positioned to control access to the river and the important trading port of Portimao.

The castle features a rectangular tower and a series of walls and bastions, with a central courtyard and a cistern for storing water. It was designed to withstand attacks from both land and sea and was an important military stronghold in the region for centuries.

In the 19th century, the castle was abandoned and fell into disrepair, but it was later restored in the early 20th century by a local businessman. Today, the castle is open to visitors and is a popular tourist attraction in the region. Visitors can explore the castle's various rooms and walk along its walls, enjoying panoramic views of the river and the surrounding countryside.

The castle is also used for cultural events and exhibitions throughout the year, including concerts, theater performances, and art exhibits. It is a symbol of the region's rich history and cultural heritage, and a testament to the enduring legacy of Portugal's medieval past.