English has these fun little verbs called "unergatives" (things like "open," "broke," or "boil").
In the sentence, "the door opened," the door is not opening anything, it itself just opened. Just like saying, the curtain moved (the curtain didn't move anything, it was moved by something else).
Basically in these sentences the "object" of the verb becomes the "subject" without needed to use the passive. Turkish does not have this phenomenon and just uses the passive. Both "the door was opened" and "the door opened" are perfectly fine here for the English translation. :)
Basically, Turkish passive=English passive OR English ergative
Umm there is a Turkish song that goes (towards the end): yaz geldi, bahar geldi, açti yeşil yapraklar. Seems that açmak can be used both transitively and intransitively (unless the line means that it's the bahar that opened the yeşil yapraklar , in which case, the example is pointless).
Examples of açmak being used transitively and intransitively: O, kapıyı açtı (trans.) Çiçekler açtı (intrans.)
(For those who love Turkish music and don't know the song yet, it's Ben seni sevdugumi ;) )