It is a particular class of passive, a "Pasiva refleja" (This is difficult, even for natives) Yes and not. The English grammar is different to the Spanish grammar. I think the categorie of you sentence (in Spanish"pasiva refleja", but not "pasiva")does not exist in English grammar. It's a mixture from "English pasive" and "English unpersonal" Is not the "pure passive". In a passive sentence, the subject receives the action (and the verb is expressed like passive) Passive. "El mar es visto por alguien" The subject (el mar) receives the action (es visto = he is seen). In your sentence, "el mar" is not the subject. So, "Se ve el mar" is a "pasiva refleja. Not a passive sentence, not a unpersonal sentence. (It's difficult, it's for an advenced level)

现代西班牙语第一册里有解释这个，叫自负被动句，翻译成中文就是：从这里可以看到海。其实中文也会有这种无人称被动的现象。

Even for us that are natives, the "se" is hard to explain

More information: English-Spanish passive: http://forum.wordreference.com/showthread.php?t=113766

Yes. Litterally it means, "From here the sea can be seen." But a better translation would be "You can see the sea from here."