The ecologist achievement is obtained by opening 5 industrial chests, which are large green chests that contain pieces of world machines. Activating a purifier, composter, or recycler also counts as one instance of opening an industrial chest.
Eminent Ecologist Achievement
Open 25 industrial chests.
Open an industrial chest by tapping or clicking on it once. You will receive a notification on screen that you've found a part to one of the world machines. Like all containers, an unopened industrial chest will have sparkles rising from it. Although sometimes found in protected dungeons, industrial chests often occur in simple underground bunkers.
You can tell if there are any unopened industrial chests by bringing up the minimap. The sidebar will display the number of parts found. Purifiers have eight parts, while composters and recyclers have six.
Industrial chests are often referred to as "ecological crates," "eco crates," or sometimes just "green crates." Don't confuse them with industrial crates, which are metallic grey.
The ecologist achievement is the only achievement with a "master" version that doesn't actually have the word "master" in its name.