Williams River is a great scenic day out, the rainforest is very pretty and the canyon has some nice slotted sections. Although there are no official abseils, it is still recommended to bring a harness and a short length of rope (~20m) as you will likely find yourself needing to meat anchor to check jumps, slides or tricky downclimbs.
Location map
Approach
Parking and Exit
Approach
Descent
Exit
Red tape
Beta sites
Fat Canyoners Williams descent from approximately 2/3rds down the page.
Trip reports and media
YouTube.com : Richard Pattison, Williams River Canyon movie