Pic of the Day: It's a long, long way down

The Yucatan peninsula in Mexico is estimated to have 6,400 cenotes, or sinkholes, and although they are hardly recommended for amateurs, they make for perfect diving pools for the likes of Orlando Duque.

The Colombian is one of the best cliff-divers in the world, and following his 27m-high jump into the freshwater pool at the bottom of Ik Kil – which is 60m wide and known as the Sacred Blue Cenote – he currently tops the rankings for this year's Red Bull Cliff Diving Series. The British diver Gary Hunt, meanwhile, lies in second place. The divers can reach speeds of up to 40mph during their falls.

Pools such as the one at the bottom of Ik Kil, near the Mayan archaeological site of Chichen Itza, exist because the land is made of porous limestone, which means that water can dissolve and erode the rock easily and collects underground rather than in rivers or lakes on the surface.