This Saturday is National Public Lands Day. Why should you care? Because you can visit the national parks free of charge.
If you don't think there is a national park near your home, think again. There are national park units in every state except, I believe, Delaware. In Iowa, you can visit Effigy Mounds National Monument. In Kansas, check out the Brown v. Board of Education National Historic Site. I should add that it isn't clear whether the fee waiver applies to monuments and historic sites. The NPLD website is horrible.