On April 22, 1970, 20 million Americans took part in demonstrations across the country demanding a healthy, sustainable environment. Those gatherings on the first Earth Day led to the creation of the Environmental Protection Agency and key environmental laws. Fast-forward to 2017, and the environment is once again in the headlines, with global warming and attacks on regulations. But today, environmentalism is more mainstream, with celebrations and other activities marking the day. Here are 27 Earth Day events that are inexpensive or free.