birkenstock women's madrid birko-flor eva slide sandals silver size 40 birkenstock the birkenstock madrid is the original that started it all. known as the birkenstock fitnesssandal in europe, this design tones the foot and calf muscles whileimproving circulation. this timeless one strap women's sandal features the famousbirkenstock contoured footbed, fully adjustable strap and shock absorbing eva sole. this birkenstock footbed of sustainable cork, featuring pronounced arch support, a deep heel cup and a roomy toe box and covered with a suede liner makes the birkenstock madrid a sandal you'll want to wear again and again.