@anderson_joshuaA turquoise ring with a dark blue centre, and the centre isn't a shadow. That's the Cetina River Spring, better known as the Eye of the Earth, sitting near the village of Cetina in Croatia. The colours come from the water's clarity, the sunlight, the rock underneath and the cave getting deeper as you go in, so the shallow edge glows turquoise while the middle reads almost black. What you're actually looking at is the mouth of a deep underwater cave system, with clear water pushing up through limestone formations below. Divers have taken the submerged passage past 100 meters (328 feet), which tells you how far down this thing keeps going. From above it looks calm, almost too perfect to be real. Underneath is a complex underwater world that scientists and cave divers are still exploring. So here's the question: would you swim out over that opening, knowing how far it extends under you? The images here are artistic recreations inspired by Croatia's real Cetina River Spring.

@anderson_joshuaA turquoise ring with a dark blue centre, and the centre isn't a shadow. That's the Cetina River Spring, better known as the Eye of the Earth, sitting near the village of Cetina in Croatia. The colours come from the water's clarity, the sunlight, the rock underneath and the cave getting deeper as you go in, so the shallow edge glows turquoise while the middle reads almost black. What you're actually looking at is the mouth of a deep underwater cave system, with clear water pushing up through limestone formations below. Divers have taken the submerged passage past 100 meters (328 feet), which tells you how far down this thing keeps going. From above it looks calm, almost too perfect to be real. Underneath is a complex underwater world that scientists and cave divers are still exploring. So here's the question: would you swim out over that opening, knowing how far it extends under you? The images here are artistic recreations inspired by Croatia's real Cetina River Spring.