The standout sight in Banja Luka is this small but gorgeous mosque, built in 1579 at the behest of Ottoman district commander Ferhat-paša Sokolović. It was under Unesco protection when, in 1993, it was deliberately destroyed as part of a brutal campaign of ethnic cleansing which saw non-Serbs expelled from the city. A meticulous reconstruction commenced in 2001, using 16th-century techniques and incorporating around 60% of the original masonry rescued from various dumps. It was finally completed in 2016.
There's often someone on hand to show you around; headscarves are provided for women. It's worth calling in to see the vivid geometric frescoes which fill the dome.