King County parks are partly reopening today. The emphasis is for people to keep moving in the parks and on the trails. No congregating or group activities. One important thing is that restrooms will remain closed, so if you tend to get surprise emergencies due to medication or health issues you may want to hold off until toilets are available again.
The list of what is and isn’t open is complicated, so I’m just providing a link to the list on the King County website. That way you can check to see if your preferred activity is open.