Letea Forest, Danube Delta, Romania (© Wild Wonders of Europe/Widstrand/Nature Picture Library)

If Earth ran on routine check-ups, wetlands like the Danube Delta, shared between Romania and Ukraine, would top the list. This vast landscape quietly filters water, absorbs floodwaters and shelters wildlife on a remarkable scale. Covering more than 5,800 square kilometres, the Danube Delta Biosphere Reserve is one of Europe's largest and best-preserved wetlands. It's where the Danube River finally slows down, splitting into channels, lakes, reed beds and marshes before meeting the Black Sea. Letea Forest, featured in today's image, is a part of this vast biosphere.