Complex sentence: The most visited area of the city, however, is the freshly renovated medieval city castle, Doboj Fortress built in the early 13th century, now houses restaurants, shops and medieval exhibitions of preserved weaponry with children's playgrounds open during the day.
Split into simpler sentences: The most visited area of the city is the freshly renovated medieval city castle, Doboj Fortress built in the early 13th century. It now houses restaurants, shops and medieval exhibitions of preserved weaponry with children's playgrounds open during the day.