The Oven of an Ovenbird (Hornero), Tumaco, Colombia

This is the mud nest of a species of Hornero, likely the Pacific Hornero. They build super strong mud nests that last for years. The big hole on the left is the passage which inside curls into a corner to lead to the main chamber. This curled construction is presumed to keep rain out. I'm not sure about the small "window" hole.

Here you can see another species of Hornero engineering a nest: