By the end of Adventure mode, I had about 4 million points. You can either play Expert mode (assuming you have 3 starred all levels), try some Challenge levels, or simply grind out the points.
For the grind, load up level 58. This is a fairly straightforward level where you simply have to free the workers and build the lava levee. The video guide I found actually took a LOT longer than the way I did it, so I will lay out the steps and try to upload pictures later if they are needed. Here is how to do it!
1. Locate the path to the glutton (bottom of the screen), you will need to clear two trees to get to him. The first tree is directly to the left of the broken bridge (bottom right). Have one worker get these two trees.
2. At the same time, have your other worker open the treasure chest that is in the smoke of the volcano. This chest contains enough materials/gold to finish the level! So collect it all!
3. Have one worker feed the glutton, and the other worker pay the pirate.
4. As soon as both paths are opened, begin repairs on the lava levee. Then click to have the broken bridge repaired.
5. Wait the 25-30 seconds for the level to finish, gain 100,000 points, then click restart until the achievement pops!