I found it interesting that one of the rarest achievements in the game was suprisingly easy to get (<1 minute of work), hence this guide. Its a bit cheesy, but fully within the game's framework.

1) First of all, you're going to want to unlock the foragers hut and banish almost every other building and technology card from the progression tree.

2) Second, you're going to start a game in 'trial' mode and choose the trial 'drafting'.

3) Now, pick the duchy and make sure that you have completed most of the faction specific missions for it, because you will need the starting resources (I'm going to assume that if you're even thinking of trying to get this achievement, you have most of the duchy quests unlocked already).

4) Using the drafting mechanic, just pick the foragers hut as one of your first buildings. Reroll buildings as much as neccesary until you get it.

5) Use the duchy's starting resources to upgrade it to level 2.

6) This step depends on chance: you're going to need to pick a map that has at least 70% forest coverage to get to the 100 gold. If you didn't get any such map for your first pick, start again at step 2.

7) Play the map and group most of the forest pieces together to use the foragers hut to its maximum effect. I was able to get enough gold in my very first run, so it's not that hard.

Voila, you just unlocked the achievement.