265 miles over 23 days in Nepal. Single day is around 25 miles while hiking in the mountains of NH. I have friends who regularly do 35+ mile days with 8000+ elevation gains.
I took the train to 125th street in Harlem and walked to West 4th street one cold day. I took my time and really enjoyed myself - I was in my early 20s and was bored and that was the budget outing I came up with for myself.
Going to google maps to check the distance.
Wow! Only about 6 miles. It seemed longer although a lot of fun.
I’ve done a few walkathons - I don’t know the distances. Maybe about 15 miles?
I’ve done the walkable bridge crossings in NYC too.
16 mile hike in Yosemite, and maybe 10 miles in San Francisco.
I almost hiked the Appalachian Trail 2 years ago, and I will hike it one day (I’ll probably have to section hike it now, as opposed to thru-hiking it like I was going to, since I’m going to be busy raising kids for the next 20 years or so :p.) Until then, I’ve done a lot of 12-16 mile day hikes. It seems like I’ve walked longer but I can’t think of any instances off the top of my head.
I walked everywhere for a long time, but probably 10-15 miles in a single journey is my max. This summer I packed stuff into a festival multiple times in a day, more than three miles in a single direction laden with heavy packs. So that was probably a good 15 miles or more in a day, loaded with anywhere from 40-70lbs of gear.
In one day’s time, it would be the hike from the South Rim of the Grand Canyon down through Indian Gardens and out to Plateau Point. That part wasn’t so bad. It was the return trip that nearly killed me. 
Holland has a tradition of summer walks, called the Four Day Walk-a-thon “Wandelvierdaagse”. Most towns organize walks of about six-seven miles (10 km) and many people walk those seven miles, four days in a row. I did when I was ten, so that is 26 miles in 4 days.
As for other walks; I’m not sure. I often take/took three hour hikes, but I walk at a snails pace, checking out every flower I pass to botanize and every bench to sit on. So, five miles on average.
A minimum of 20 miles, hitchhiking from Dover back towards London. We didn’t get a lift until we hit the services on the M2. I think my mate and I must have looked a right shady pair , so I’m not surprised no-one stopped for us. 
Longest single hike I ever did in a day was Mount Whitney up and back which is about 21-22 miles. I did a 25 mile “fun run” a few weeks ago and will be going farther.
FWIW when I was snowcamping one of our instructors is a friend of the fellow mentioned in this story:
He was averaging 30+ miles every single day for over 300 consecutive days. Dean Karnazes did 50 marathons in 50 consecutive days (in all 50 states) a little while back and IIRC 100-mile runs are typically won in under 24 hours. My latest edition of “Fixing Your Feet” has some sections on people who have done ultra-long distance runs and walks, including a guy (don’t have the book in front of me so no name) who started out at 300lbs and walked across the US to get into shape. Point of all that being that people can do some incredible feats of endurance and they aren’t all amazing athletes.
Makes a heckuva lot more sense. That brings things down to 30+miles / day. Not something I’m in the shape to do, but something I could conceivably be in good enough shape to do.
Valgard, the achievement in that article is impressive. I know one person who has hiked both the AT and the CDT (and not in the same year, either). One thing about most “ultra-light” hikers, though, is that they usually don’t carry much gear, at all. Not to diminish the pace they keep, but, in order to do so, they’ll usually arrange a whole crew of folks to drop off food and gear for them on a (nearly) daily basis. Still 7,400 miles in (less than) one year is impressive as hell, any way you slice it.
Once, due to being out late in Tokyo after the trains stop running and without enough money for cabfare, I tried to walk home from three train stations away. It should have been maybe 4 miles, tops. Instead, I got lost, walked way out into the country (I never did find out where I got to), and ended up walking for 6+ hours at top speed, so I figure at least 22 miles.
The highlight was finding an open Koban (police box) at 3 or 4am and asking which way to Akabane; it wasn’t even on their local map, it was so far away, but they were able to point me in the right direction (which was mostly backtracking the way I had come).
Since the trains started around 5:00 or 5:30 am (or earlier? I don’t remember, this was a long time ago), I would have been better off just hanging around and waiting for the first train.
Roddy
I can’t think of a longer walk for me than about 15 miles around NYC starting from and returning to the Staten Island Ferry as an overweight 32 year old.
I biked over 40 miles as a teen for the fun of it and I often took 20 mile bike rides but I was never much for hiking. The biking sadly stopped when I got my license. This was not a smart decision.
I just had a thought. Two years ago I spend 5 days in Chicago and I walked a good 30 miles over that 5 day period as a fat 40 year old. I got to meet Mr. Bus Guy at least.
About 140 miles, from Tacoma, Washington to Portland, Oregon.
How long did it take?
Went for a couple of months without any mechanical transport in the ARMY way back when out in the bush. No idea of the total distance.
I have heard that the old Iroquois Indian message runners in the 1600 hundreds could do 100 miles a day every other day.
YMMV
My longest single day was 44 miles pretty much just for the hell of it when I was in high school
In the early 80s I made the length of the Wind River Mountains in Wyoming, something like 120 miles in 8 days.
My longest cannot compete, but within recent memory, the longest I have ever walked was when I did some hiking in the mountains for a total of maybe 50 or 60km.
What felt like the longest but was nothing by comparison was when, after a very late night of drinking, my friend and I decided that we had had enough with the Roppongi scene (we were both only there because our mutual friends liked it there) and decided we were going to walk. I don’t think we had a real destination in mind, but we ended up stumbling around Tokyo around 2 or 3 in the morning until, hours later, we found a 24h curry house that we recognized, had a plate of curry rice, then wandered into the nearest karaoke box to crash for the night. We probably only walked 10 or 15 km or so, but it definitely felt like forever.
Not sure the mileage…nor the elevation gain/loss but it was A LOT. probably averaged 1/2 mile +/-vertical change per day every day. trekked alone in tibet for nearly 2 months by myself with a 45 pound backpack 20 years ago. i did other tibet treks but that was the longest one.
I once walked from Filey to Whitby along the Yorkshire coast–it’s about 22 miles and I did it in 3 days.
Maine to New York once. I might have known then how far it was. I have no idea now. I know is stopped being fun in Massachusetts.
Longest in one day was 25 miles “Hike for Hope” (Hope was a hospital ship of some kind, late 60s or early 70s.