According to Wikipedia, Kruševac Fortress was a fortified medieval town that is first mentioned in 1381 and changed hands between Moravian Serbia, Hungary, and the Ottomans over the following century.
Today, only limited ruins of the original fortress survive,
The only reason I’ve heard of the fortress is this photo that occasionally pops up on Reddit and other forums showing a unique way of presenting the ruins to visitors.
This is a fascinating way to allow visitors to visualize what the area once looked like. This is one of the few use cases where I’d enthusiastically embrace augmented reality as solving a real problem.