Most storybook trolls aren’t known for their friendliness, but one group of real-life wooden trolls is doing a very kind thing. The trolls, along with the artist who makes them, are trying to teach humans how to take better care of the planet.

Danish artist Thomas Dambo and his team have created more than 150 troll sculptures using old wooden boxes, pallets, furniture, and more. The giant trolls are located in more than 20 countries, including 21 U.S. states. No two trolls are the same. Dambo’s website includes a helpful troll map with information about each troll, including its name, its story, and where it can be found.

The trolls are fun, but there’s a serious message behind them. Humans throw away tons of garbage every year. Dambo’s use of recycled materials is meant as a reminder that we all need to reduce the amount of waste we produce.

“I believe that we can make anything out of anything,” Dambo told the Associated Press. “We are drowning in trash. But we also know that one man’s trash is another man’s treasure.”

Trolls have been story characters since well before books existed—a time when people told stories aloud. The creatures are said to live for thousands of years, which means they will have seen the effect that pollution and waste have had on the planet. Dambo says most of his trolls don’t like humans because of what they have done to planet Earth.