Two tiles to the left from where start you game is an invisible town. Visiting there MAY improve your chances of surviving this monstrosity.

Despite being labeled from "first" to "last," you can obtain these cards in any order you choose.

1st Card: Roughly North of Lotar Village (the one that's actually visible on the map, and has an old man who will tell you about the card keys to begin with), There is a pathway that appears to look like different mountain tiles from the rest. This area is actually passable, if you haven't figured that out, and it will lead you towards a desert. Save and restart often as you travel through the desert, because there are several tiles that warp you to a dungeon, which not only has some brutal encounters, but the end of that dungeon will randomly warp you to a place far away from where you need to be. You want to aim for that red door Northwest of the desert.

From here, you should be taken to a confusing area filled with grey squares. To save you your time, from the tile where you first enter the dungeon, Go 7 steps to your left, 5 steps up, and 2 steps left in that order. You'll a card key at that last step.

2nd Card: Head East from the same town of Lotar, until you find a huge forest below your position. If you haven't figured out how to cross through the forest maze from hell, here is the layout of the entire maze:

The blue dots mark tiles that will transport you to a forest dungeon, and just like the desert dungeons, they too will send you as far away from this map as possible, causing you to have to walk all the way back again. So avoid them.
After clearing the maze, head to the door and you'll be transported to a cave. Take any path BUT the upper path; it'll lead you to a dead end. Then, continue onwards until you find a set of rocks arranged in a square, placed between the cave river and having a gap in the center. Walk over it (it's passable), and once you reach the T-junction, take the upper path, and continue heading up until you are transported to a hidden spot on the world map. The second card key is on the green tile you'll find there.

Final Card: Continue through the cave, only now you are taking the bottom path instead of the top. Head for the door to exit the cave to reach your next arduous destination. From here, you'll start to see some mossy green tiles, these tiles will damage you, and unless you have a huge amount of potions to constantly keep yourself alive, there is no way to pass it without dying... So instead, take a hidden path around the whole death trap starting from a gap within the grey walls that separate the tiles you are one from the ocean.
After clearing that pathway, there will be a town just ahead of you, but you don't need to go there. Instead, look for a hidden passageway that'll be southbound from the entire path, you'll know that you are on it when you stumble upon a part of the grey wall that you can walk on. Continue down this path until you reach a desert area. Continue Eastbound, and somewhere towards the center of this path is the invisible desert town of Psalm.
Here is when things get a bit tricky, you start at the outer walls of the town. DON'T walk away from the town or you'll have to do this whole thing all over again. Continue walking down, and where you see the yellow-green and orange "road" directly touch the blue "wall", walk to your right towards that road and you'll enter town. Hopefully, you'll have keys prepared to open the doors here. head towards the Northeastern corner of town, where an old man dressed in red will reside. Talk to him to receive your final card key.

*whew* God I've created a monstrosity. xD