21 miles I think. It took all day. In my hitchhiking days I walked across several towns in Colorado, unable to get a ride. I don’t know how many miles. 15 to 20, I’d imagine, for some of those trips.
From the Presidio along Lombard Street to Coit Tower (I did take the elevator to the top of that).
Then all the way down Montgomery to Market
Took the BART a couple of stops, down to Civic Center,
Then walked up Haight to the Red Vic at 1665.
Not as long as some walks reported here, but I think you should get bonus hill-points for San Francisco.
It was at an Ontario provincial park. We went on the longest hike (supposed to be 7 miles) and got thoroughly lost. The little map we left behind had looked too mickey-mouse, and these trails are well sign-posted, right?! Hours later, that little map helped us determine the 20-mile route we took. Slept well 
20 miles to school everyday
in the snow
uphill
bothways 
Did about 22 miles in two separate trips in one day in the Army. Not a forced march, just a couple of map/navigation practices, we walked at a nice, comfortable pace. We weren’t wearing full packs but we did have combat gear on (webbing, with the canteen and magazines and crap, not wearing helmets but carrying them on our backs, and rifles.)
It was a nice day, perfect for a long walk. Coulda done 30 miles, maybe 40, easily.
Infantry.
That I’m sure of, 11.5 miles from my house to my boyfriends. Probably more when I was walking around everywhere in Israel.
About 21 miles. Got a wild hair and decided to hike the Pine Mountain Trail in central Georgia. Only carried a day pack and water. Not too bad. Cold beer and hot shower later felt pretty nice though!
Twenty-six point two miles, baby!
After that, I’ve run four half-marathons, each of which would have been 13.1 miles.
Running aside, my single longest trek on foot was probably from Amicalola Falls to the start of the Appalachian Trail at Springer Mountain in Georgia. I think that was ~15 miles.
Once hiked about 20 miles through Yosemite in 8th grade. That was killer.
Also walked all the way across San Francisco, from the CalTrans station to the Marina. With lots of detours along the way (my sense of direction is…well, I don’t have one). Not exactly sure how long this is, but it took several hours. Plus, the aforementioned bonus hill points.
I’ve also hiked, over a period of four days, from the Mediterranean Sea to the Sea of Galilee. I think we covered about 18 or so km a day (it’s further than that, but we had busses).
This one pales in comparison to my other long walks, but I once walked about 8 km from a campground to a waterpark in Israel. The notable factors were that we hiked on the beach, it was extremely hot, and I had forgotten to apply sunblock. Owwwwwwww.
looks like I’ve gotten everyone here so far. I’ve done the JFK ultramarathon in Western MD. Total course is 50.2 miles over the mountains and along the C&O canal. I’ve been thinking on doing it again but I’m WAY out of shape right now.
Hey!! I was there, too! Walked all over San Francisco as I recall, but I don’t remember how far. I want to say 30. That was in the early 70s, right? Maybe 71?
I’ve climbed one end of the Sandia Mountains near my town, walked the length of the crest and down the other side (down is by far the worst part), and I think that’s about 32. I’ve done that about five times and I keep forgetting how miserable I feel during the second half.
Oh, and I’ve run 26.2 miles.
I’ve done a couple of orienteering events years ago where we did something like 50 miles over a weekend.
I’m gonna mention my best cycle ride even if it has nowt to do with owt.
I’ve done 217 and 219 miles in 12 hours - in time trial events.You can’t imagine how much that hurt.Also did 260 miles in 24 hours but that was just for fun.
I once did 25 miles sponsored walk/jog with a (not too heavy but noticeable) backpack.