Atlantis: The portal is in SouthPole. My tip to find it: fly up when you first get there and look around until you see a glowing portal, it should be in one of the corners of the map.
LastCave: The portal is in Atlantis, go straight down to the bottom edge of the map and then go underwater. It is in a cave towards the bottom of the ocean close to the center of the bottom edge of the map. (I hope this wasn't confusing)
SkysRim: this is the hardest map to get to. The portal is all the way up in Ascension Island. When you are in Ascension Island, go up the platforms that go way up in the sky. These platforms are what makes getting to Skys Rim the hardest. There is a key to get up all of them:
1. Go up all of the rectangle platforms until you get to the circle platforms.
2. Right after the platforms change to circles, there is a fork. Go up the left side.
3. Keep going up the circle platforms until you see some that are starting to go down (they will be on the left side), go down those until they start going up again. All of them are in a straight line, in line with the first platform you jumped down from.
4. Keep going up the circle platorms until you get to the ring platforms. These are the hardest.
5. My tip for getting up the ring platforms, jump from the sides of the rings onto the next ring. The next ring's side should be right in front of you. I read somewhere there are 12 of these.
6. After the rings, you have to jump on two more bigger platforms with the second one being the one with the portal.
What makes this map hard to get to is, you cannot fly in Ascension Island so if you fall you can:
1. Start over from the bottom.
2. Try to land on another platform below you.
3. Set your home spot at several spots on the path. This is what I did to get up there. My advice: set the home every couple levels higher you get + at where it changes as described in the steps above. And for the rings section, set your home every time you get onto the next ring. It is tedious but it's easier than having to do the rings all over again.
Once you get to Sky's Rim, I suggest setting your home spot there in case you want to get up there again. That way you won't have to go all the way up Ascension Island. And once in Sky's Rim you will be able to fly.
I hope my tutorials helped, if they are confusing or you can't figure them out, there are several videos showing how to get to each map.
