Suggestions for 25th anniversary trip?
 

So we have a significant anniversary coming up in August, and would like to take a 5 day trip in the US. We went to Seattle for #20, and have been to San Francisco. Not interested in the beach, and can't do a lot of strenuous walking.
Home airport is ATL.

North East? Boston, New York, DC?

Fly to Portland or San Francisco then take a cruise to Alaska.

Agree + New England

Excellent suggestion if OP has the time off to do this. :)

If you can broaden your horizons to the rest of North America, Montreal is a lovely destination.

Suggestions for 25th anniversary trip?
 

Portland Maine.

5 days is too short for an Alaska cruise.

Montreal is a great summer city, although when we were there we did walk a lot. Same goes for Toronto...I love being there but I almost always do it without a rental car and end up running and walking 15,000+ steps a day.

Finger Lakes, NY
Cape Cod, MA
Vermont
Maine

All of those would be good in August, done with a rental car and minimal walking. We fly in/out of BTV whenever we go to Quebec, but never actually spend much time in VT. It looks wonderful...would love to spend 5 days there...

Continuing OP's trend of Western US cities, Portland OR is very nice in August. The city offers many sights that are walkable-- easy walking, not strenuous. The light rail and taxis/Uber offer good fallback options. In addition to spending a day or two seeing downtown's many sights, spend a day driving the Columbia Gorge, a day driving out to the coast, etc.

If OP wants to stay a bit closer to home (2 hr flights from ATL instead of 6) I second the suggestion upthread of the NY Finger Lakes region. Summers are beautiful up there. Warm days but rarely hot, pleasant evenings that seem to stretch on forever. The area is very driving oriented but is dotted with numerous small parks that offer a mixture of easier and more challenging walking trails.

We like the idea of a couple of days in Portland, then taking the train up to
Vancouver, BC. for another couple days, and taking a ferry back to Portland. Is the ferry a good option, or stick to the train?

San Diego!!!!!

Sea World + Penguins + USS Midway + lots of US Navy boats + great food + Great hotel (US Grant | Luxury Collection) + great weather!!

A ferry or train to Vancouver seems more like something you would do from Seattle as opposed to Portland, OR. Perhaps if you want to see BC you could base your trip around Vancouver and do a side trip out to Victoria?

Also, if you're now extending "in the US" (which you wrote in your original post) to include Canada, I'll suggest a trip to the beautiful national parks of Jasper and Banff in Alberta. Drive between the two and make sure to stop at the Columbia Icefield along the way.

Man, I just think the ATL-West Coast trek for basically a long weekend has a high travel-time-cost to it.

5-hour flight (if there's a nonstop), trains, ferries, etc...all of this sounds awesome if they can make it a two week trip.

Otherwise, take a DL nonstop up into the Northeast to a small/mid-sized airport and go from there... Your 5-day trip would only have to give up the first morning and the final evening to the act of getting there and back.

There is no such ferry. There is a passenger-only high-speed boat shuttling between Seattle and Victoria though:

http://www.clippervacations.com/seattle-victoria-ferry/

The ride is pleasant in summertime and Victoria is well worth a visit. (It's on Vancouver Island, not to be confused with Vancouver itself which is on the mainland.)

Suggest you consider flying to Portland, having a stay, then taking the Amtrak Cascades up to Seattle, see the city for a day or two, then get over to Victoria on the Clipper, perhaps availing yourself of one of their inclusive ferry + hotel packages. After that you can either fly home from Victoria or take a bus/ferry package over to Vancouver to have a look, then come home from YVR.

If you like trains, a very nice trip would be to fly to Toronto and take the Canadian across Canada to Vancouver,. The train leaves around 8 at night and you spend four nights on the train, arriving in Vancouver in the morning. You could then spend a day or two there and fly home from there or add a bit more time and train or ferry it to Seattle and fly from there. We did this a couple of years ago and it was wonderful. However, be sure to spring for the bedroom on the train. I love New Emgland but places such as Portland, ME are zooey in August. One year my husband and I went to Islesboro in Maine. It's an island about 3 miles from Lincolnville with ferry service from there. You could spend a couple of days in Portland/Camden during the week and then go to Islesboro where it is very peaceful and beautiful. Another lovely trip is Asheville, NC but that may be too close to you.