Depending on where you live in the Seattle area there are many urban parks on the bus lines and/or a short Lyft/Uber from downtown including Discovery Park, Seward Park, Sculpture Park, Alki Beach, Carkeek, Greenlake, + more. There is also Drive Now or Car 2 Go and there are some amazing hikes a short 30-60 minutes away. Parks like Mt. Rainier or Olympic National Park would require you to rent or borrow a car. Depending on how frequently you plan to go there are a lot of outdoorsy meet ups and there are often opportunities to carpool. Hope this is helpful!