Once you have the Missinglasses, you will be able to reach the Palace, which is the final dungeon!
Enter the Palace
Go to the Palace, which is marked on the map after you have obtained the treasures from all eight dungeons. To enter the Palace, use the Missinglasses to reach a water tile to the right of the palace. Get into the water and press the dive button to dive. You will enter the underground passage into the palace. Keep following the path to find a ladder up to the palace proper.
Go down a few screens until you can't go farther down, then go to the right. Enter the door on the right. You will find Prince Daniel, who tells you to find the blue key in the jail. (For a shorter route, from the bathroom, use the Missinglasses to wrap around from the bottom of the screen to the top, then go up two screens.)
Get the Blue Key
From the screen with Daniel, go one screen to the right, then enter the cell on the left and use the Missinglasses to go to the left and wrap around to the right side of the screen, but avoid the blue tiles along the top, as they will teleport you to another room. (If you do get teleported, you will end up standing on a ladder, which you can climb to return to the first floor, where you can go downward and then left to find the entrance to the jail. There is also a cracked wall in the room you get teleported to, which you can break open to wander around the dark areas of the map.)
From there, go to the right, and in the next room, use the Missinglasses while walking left to wrap around to the right side of the screen and get the blue key. Then unlock the door below you, and go to the left and unlock the door there, then go left to the next screen.
Use the Missinglasses to wrap around to the left side of the screen, then unlock the blue door to get the treasure in the jail cell there.
From here, you can make your way back to the main area, where you can see the green key. There is also a blue lock block that you can optionally unlock to find the crypt.
Get the Green Key
Back in the main room, go to the left from the screen where you can see the green key. There are red carpets in the shape of an arrow pointing down. Use the Missinglasses to walk upward and wrap to the bottom of the screen where the arrow is pointing. From there, you can walk downward to a new area.
You can kill the snail here if you feel like it. Although it seems like this is a dead end, you can use the Missinglasses to go up through where the door is, to wrap around to the bottom of the screen. Then, while walking in the dark area, walk to the right side of the screen, and use the Missinglasses to walk to the right so that you end up on the bottom-left path, with the table and stool. Go left from there to the next screen.
In the screen with the couch blocking the path, use the Missinglasses and go to the right, to end up in the dark area at the bottom left. Go down to the next screen.
In here, go as far to the right and down as you can go, then use the Missinglasses and go up. Then use the Missinglasses from here to go to the stone path up above, and kill the skeleton spider on that path. Then wrap back around to the bottom left path, and use the hammer or a bomb to break the cracked wall above the square of red carpet. Go through the door you revealed, then go to the left (careful not to step on the blue tiles), and go down to the next screen.
Break the cracked wall of the bottom-left room, then kill the skeleton spiders in that room. The right wall has a crack in it, too, so open it if you feel like it. Then walk to the right, so you are up against the middle path, and walk upward to the previous room.
Wrap around to the upper middle platform and kill the skeleton spider there. Then wrap around to the stone platform at the bottom of the screen (the blue tiles won't teleport you), and kill the skeleton spider there.
Now you can go downward to step on a blue tile to get teleported to the ladder room. Climb the ladder, then go downward until you can't go farther downward, then go all the way to the left, and wrap around to the bottom of the screen where the arrow of red carpet is pointing. Go down to the next room.
Wrap upward to reach the bottom of the screen, then wrap to the ledge with the table and stool, and go downward to the next screen. Kill the skeleton bats, then go to the upper right and use the Missinglasses there to wrap to the bottom right, then go up and right and use the Missinglasses there to wrap to where there is a red carpet and two pots. Go to the left from there, then make your way downward until you find a ladder. Climb it, then go up to the next screen, and use the Missinglasses here to wrap around to the top of the screen. Then go up to the next room.
Finally, use the Missinglasses to wrap around to where the green key is. Use it to open the doors below. Then exit to the north.
There are two skeletons with axes. Kill them both, then go up through the door. From here, you can go to the upper door and jump over the hole. Once you go through this door, you will be prompted to save, and a battle will ensue, so make sure you are ready before proceeding. You may wish to read the Endings page before you continue.
Once you go through the door, you will face the Chairman.