Salasel Castle in Shushtar, Iran, dates back to the Achaemenid era and served as a key defensive fortress and administrative center controlling the Daryoun River and the surrounding region. The castle spans around 5.3 hectares and once featured numerous yards, towers, gardens, stables, kitchens, barracks, and baths.

Although much of its original structure was damaged or repurposed over centuries, including significant destruction during the early 14th century, the remaining underground chambers and tunnels highlight its architectural and historical importance. Salasel Castle is part of the Shushtar Historical Hydraulic System, a UNESCO World Heritage site, reflecting its role in managing water resources for irrigation and defense.

The castle was reconstructed over time, with visible ruins dating mostly from the Qajar period, and remains one of the area's most significant cultural landmarks.