Multnomah Falls is a must do destination when in Oregon, but until recently was only accessible by car or tours.
In recent years, CAT introduced the Gorge Express which takes a mere 25mins from Gateway Transit Centre.
Gateway TC is easily reachable my Max Lines and buses, from as far as Downtown and the Pearl District in Portland.
The Gorge Express costs 10 USD one way and runs every hour or so.
Be sure to have cash on you to pay the driver and off you go.
You will be dropped off in the car park. Note Hood River bound is a different stop to Portland bound, yet both about 3mins walk through the underpass to the falls.
On arrival rember to get the Multnomah Falls Tour/Transit Access sticker from the driver which allows you entrance to Multnomah Falls.
Visitor numbers are monitored so best time to arrive is the morning to avoid queues and a wait.