It's beach time and I bet you will see more of these out by the pool this year.

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They are called barefoot sandals. They are really just jewelry for your feet.
They can be tied either at the back or the front of the foot.  You can get them in all kinds of varieties from the very simple the the extravagant. Most of these barefoot sandals (they have no bottom) will cost you about 12-20 dollars. But you can make your own. Here's a video giving you step-by-step guidelines.