German police deployed hundreds of officers in and around the western German village of Hochneukirch to prevent demonstrators from blocking the vast, open-pit mine and adjacent power plants.
Hundreds of protesters succeeded in temporarily blocking railroad tracks used to transport coal and another group broke through a police cordon and entered the mine, German news agency dpa reported. The various rallies were mostly peaceful.
The mine has become a focus of environmental protests in recent years because the operator, German utility company RWE, threatened to chop down a nearby forest to enlarge it.
"It's important to increase the pressure on the government," protester Selma Schubert said. "The government doesn't do enough against climate change."
Participants in the Saturday protests held banners calling for climate protection or singing songs as they marched through villages in the Rhineland region near the mine.
According to German environmental group Bund, more than 8,000 people took part.
"You're building a movement, that's beautiful," said protester Seimi Rowin, who came from Scotland. "But we need to get to the next step ... otherwise future generations will pay for it."
Following months of climate protests by students and a sharp rise in the polls for Germany's Green party, Chancellor Angela Merkel recently threw her weight behind the goal of making Germany climate neutral by 2050. That would mean the country's economy no longer would add greenhouse gases to the atmosphere.
Scientists say ending fossil fuel use by mid-century is a must if countries want to achieve the 2015 Paris climate accord's most ambitious goal of keeping global temperatures from rising more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) compared to pre-industrial times.