Judging by all above ignorant negative comments, how many of you really owns a genuine pair remains to the question. Sour grapes. If u don't understand and can't afford the high price for such sandals, suggest u to dig some research before making a fool out of yourself.
Regarding the "this shoes meant for indoor" comment, I find it hilarious. No European slippers or sandals are specially made for indoor or outdoor purpose. Just wear it whenever and whenever u like. Birkenstock comfort emphasize on arch. It is design to fit perfectly on your feet. Not for cushioning purpose.

Not sure if Birkenstock owners here really wear it with such cautious in mind. At least not me. It's a slippers bro. Not a phone.
BTW, don't think u want to wear any slippers for hiking either.