Lipa Cave is one of Montenegro's easiest major cave visits, with guided tours through cool karst passages close to Cetinje. Stalactites, stalagmites and underground chambers give a very different texture from the royal museums and monastery courtyards in town.
The cave works well as a half-day addition to Cetinje or Lovćen. Bring a layer even in summer, and check tour times rather than assuming continuous access; the underground route is managed and guided.