Not that there's much to recommend it, anyway. It's uninhabited and 90% of its surface is covered (thank you, Wikipedia) by a fort which was erected in the 1850s and used during World War II as a concentration camp. It makes a good setting for a horror movie, I guess.
2013's Killer Mermaid is a Serbian film in which two American girls traveling in Europe meet an old college friend who talks them into making a little excursion out to Mamula to check out the military fort. A Creepy Old Guy warns them not to go, but they ignore his warnings--and decades of murdered tourist movies--and go out to Mamula with their friend and his fiance.
The looming love quadrangle is cast aside when they witness an elderly man dump a bucket of--what, blood?--into a well in the floor. The blood is followed by a couple of severed hands, and our protagonists have a hard time holding in their revulsion until the guy is out of earshot.
What follows is a pedestrian stalk-and-slash horror film which should have had a twist at the climax, but doesn't. The Old Guy (who has a name, but I've forgotten it--he looks like a young (70ish) Fidel Castro)) pursues our heroes through the tunnels under the fort, dispatching them one by one. They find a room plastered with newspaper clippings reporting disappearances, and realize that they've stumbled upon the lair of a serial killer. Then the Creepy Old Guy from two paragraphs ago shows up and dumps a bunch of exposition: the fortress is home to a mermaid, an ancient creature of the sea, who feeds on unsuspecting land dwellers. The Other Old Guy is enslaved by the mermaid's wiles, and it's his job to capture food and bring it to her. The two Old Guys have some history together, but it's nonsense and not worth getting into.
This whole movie is nonsense. It was brought to my attention by somebody whose one-sentence review was "...then we saw Killer Mermaid, and that was really something." Really what? Really formulaic? I'm only just realizing that he may not have been endorsing it.
There's nothing special about Killer Mermaid; it's not good, nor is it superlatively bad, but the film's biggest asset is that it appears for 2/3 of its runtime to be a simple slasher movie set on a remote island, and then the mermaid shows up. The mermaid should have been a surprise, and I assume that she was intended to be. The Serbian title of this film was Mamula, and Killer Mermaid was applied for the English language release. It's being distributed in America under the title Nymph, but that, too, spoils a little too much of the secret. Mamula is a better title, even if the average American doesn't recognize it. I might have called it Fort Murder, which strikes me as a better title than than Killer Mermaid, and it's still a bad title.
Here's the trailer.