Located on Montenegro’s Lustica Peninsula, the Blue Cave is one of the country’s most popular attractions. Also known as the Blue Grotto, it derives its name from the iridescent blue water that is reflected throughout the cave. The largest of several caves on the peninsula, the Blue Cave features clear, warm water about five meters deep that is great for swimming or snorkeling. Indeed, many say you need to see the water underneath the surface to truly appreciate it. With a ceiling about nine meters high, the cave is a popular stop for tour boats, most of which will give you about 10-15 minutes to take a quick swim.