The Marine Drive multi-use path is a sweet little section of biking/hiking/walking and generally anything-without-a-motor-ing path that hugs the Columbia River from NE 33rd out past the I-205 bridge. It's mostly flat and set down a bit from Marine Drive in many areas, so while on the path you definitely feel like you're out on the river. However in some areas, like near the airport, it's set up above Marine Drive, offering fun views of aircraft landing and taking off, etc.
I've biked this path a few times on the section between 205 and the airport. On weekdays during the daytime it's pretty deserted. As this path connects with the 205 Multi-Use Path, it offers a lot of miles of fairly un-interrupted dedicated paved path for riding. The zero inclines along the path add to ease for family outings. There's pretty much no cover from the sun, however, so anyone planning to go the distance on this path should definitely be rocking the sunscreen, especially with the water right there next to the path.
There are some spots available for parking along the length of the path however I've always accessed this path via the 205 connection, which you can take across the river to Washington (exhaust is an issue) or down south all the way to Oregon City. All told, this is part of a much larger system of trails that lets you stay out of traffic and get some serious mileage in.
As an added bonus, once you get east of the 205 bridge, the views of Mt. Hood up the Columbia are stunning. read more