Antibubbles are a common but widely unrecognized phenomenon, in part because of their resemblance to air bubbles, and in part because of their typically transient, or short-lived, nature. With certain (soapy) solutions, they can be made to last much longer.
Antibubbles can be created by allowing a tap to drip into a container of water to which a drop or two of soap has been added. They have all been produced aided by an ultrasound contrast agent. Being inherently unstable, they are difficult to form.
The soap reduces the water's surface tension and allows the skin of air surrounding the droplet to remain in place for more than just a fraction of a second. As antibubbles can be easily  created at home, they have attracted attention from popular science magazines.
Just as soap bubbles, with air inside and air outside, have negative buoyancy and tend to sink towards the ground, so antibubbles, with water inside and air outside have positive buoyancy and tend to rise towards the water surface.  But again, just as soap bubbles can be filled with a lighter gas to give them positive buoyancy, so antibubbles can be filled with a heavier liquid to give them negative buoyancy.  Using a drinking straw to drop droplets of sugar solution onto soapy water will produce antibubbles that sink.
Antibubbles usually pop when they touch the bottom or the side of the vessel containing the liquid.  This can be prevented by tipping a few teaspoons of sugar into the soapy water and giving it some time to dissolve (but without stirring it).  This will produce a denser layer of sugary water at the bottom of the container.  Antibubbles made from sugar solution will then sink through the water and rest on top of the denser layer at the bottom.  Antibubbles made this way can last for several minutes.
The layers of an antibubble are water, which it is submerged in, air, and the water trapped in the air.