Skip the drive to the mountains this week (it's still muddy up there), and hit the hills closer to town. Littleton's Audubon Center is celebrating its 40th anniversary with walks through the wetlands and kids' bird-watching hikes, as well as a plethora of other nature activities. If you prefer a mellower wilderness experience, drop in on the Audubon's classes on bird photography or coyotes, hit up the wildlife photography show, or simply grab a slice of pizza. This all-day festival has an activity for everyone. Sun, June 7, 10 a.m.-4 p.m. Audubon Center, 9308 S. Wadsworth Blvd., Littleton, 303-973-9530 Free