Madrid Birkenstock Madrid This simple one-strap style was designed as an excercise sandal because your foot flexes and grips the toe bar while walking, promoting good circulation. You can wear is as a casual summer sandal as well. Menorca Birkis Menorca One strap is all you need to keep this spunky sandal on yet keep your feet cool in warm weather. You'll get great arch support from the anatomic cork footbed and the deep heel cup keeps you stable while walking.