I've decrypted the pictures of the trees into what are probably coordinates, using the center picture as a map,
it seems to be a base 10 system, with a base 5 semibase, causing the background trees.
The coordinates I get are
35.992862, 19.264688 which puts us a ways off the coast of Greece, which seems like as plausible a location for Atlantis as any.
The 'Keys' I imagine are additional pieces of information that need to come together to actually gain entrance.
The first one looks a lot like Pi, and the second seems to be translatable to the English Language alphabet. "W Y V T Q J W B E E V J Z B F M P N F V T M X G S J O C L S B Z H X K O L W U N Y R R P"
or, as pointed out in the comments, XZWURKXCFFWKACGNQOGWUNYHTKPDMTCAIYLPMXVOZSSQ
I've tried a few ciphers on the second set, but haven't found anything worth mentioning yet. It's only one symbol longer than a spaceless version of the words on the gate, but I haven't been able to make anything come of that either.
Although... there should be a connection between keys, trees, and pi.
I see it! A Key Lime Pie! Bring one to the coordinates in question, feed it to whoever you find there to look the other direction, and break in with a sledgehammer!