Photo: EncMstr, CC BY-SA 3.0 Free nature spots in Portland
Photo: EncMstr, CC BY-SA 3.0 
Photo: EncMstr, CC BY-SA 3.0 Forest Park
Free, always
Photo: EncMstr, CC BY-SA 3.0 Hoyt Arboretum
Free, always
Photo: Cacophony, CC BY-SA 3.0 Mount Tabor Park
Free, always
Photo: John Fowler from Placitas, NM, USA, CC BY 2.0 Multnomah Falls
Free at certain times
Photo: Jmchuff, CC BY-SA 4.0