Nebulae are clouds of gas and dust, and there are untold millions of them in the galaxy. Some are tiny, just knots of material, and others are vast, sprawling across many light years, with complex structures and histories.
One such nebula lies about 5,000 light years away in the constellation of Sagittarius. It goes by many names: Messier 17, the Omega Nebula, the Swan Nebula… it's so big and bright that it's an easy target with binoculars, and through even a modest telescope the looping "omega" shape that gives it one of its names is obvious. Inside that is a brighter patch of gas that does indeed look like a swan (though usually upside as seen in photos); I've seen this myself at the eyepiece.
That part of the nebula is a star factory. Hundreds of stars are being cooked up inside the cloud, star birth set to mass production mode. Small clumps of gas and dust are collapsing, forming dense cocoons around stars just starting to ignite the thermonuclear fires in their cores. From the outside and in visible light these look dark, their thick shells blocking the nascent starlight within.
But if you look in the infrared, outside ...