The longest walk for me would be ~35km on Day 1 of the Weekend to End Breast Cancer in Toronto. We followed that up with ~25km on Day 2, which makes the two day total a whopping 60km. I was very sore afterwards. 
I love taking long walks - in summertime, it’s not unusual for me to go for a 10km walk on a weekend day, just for the heck of it. When travelling in a walkable city like Barcelona or NYC, I’ll usually average around 10-15km a day while sightseeing.
27.9 miles in high elevation to visit Macchu Picchu. That was killer. But well worth it.
About 1700 miles from Baxter state park in Maine to Perisburg VA on the AT. 5 months in 2007. Longest single day would have been around 35 miles, but that was really pushing it.
Nonstop (no eating, sitting, etc): 46 miles, round trip on foot from Queens Village to Huntington Station.
Over the course of days with opportunity to eat, sleep, sit down, rest, etc… yeesh, I dunno, I did the Boy Scout thing, and our family did a lot of hiking around in the Pecos Wilderness of NM, those 5-8 day excursions of 10 miles +/- per day… it sort of leaves itself open to interpretation after awhile. What defines a ‘session’ ?
Was that the regular Army, or the acronymic U.S. ARMY (=“Uncle Sam Ain’t Released Me Yet”)?
Me, hmm…probably 10-12mi in a day once or twice. Lately, 6 mi, the length of the Vancouver Seawall, a couple summers ago. (I assume it’s still the same length.)
Okay, if we’re not counting in a single day, I walked from the Mediterranean to the Sea of Galilee over a period of 4 days. It was a rather posh little tour, though, we had buses cart us to our camping spot (we camped in the same spot two days in a row at one point) and I can’t guarantee I walked the entire way, but it was definitely most of the way.
Okay, I just googled that, and apparently it’s only 27 miles. What? That must be as the crow flies. There’s no way it was a 27 mile hike the way we went. I don’t know.
10 miles. I intend walking the marathon in October 2009 but I don’t know whether I shall complete it or not.
I got stuck in traffic a few months ago and decided to get out and walk. It took seven hours. I’m not sure of the distance I covered.
I hitchhiked from Grand Junction Colorado to Homer, Alaska. My Longest walk was form some park station near Lake Jenny In the Grand Tetons to Gardner Montana. I remember the Official at the ranger station asking how I was gonna get there snowshoe or ski. I said snowshoe I had neither and was drink most of the time. I had no idea what I was getting into. It was march or april I don’t really remember. I post holed it a really long time to the lake. Got drunk woke up and hiked out all the way to Gardner through Yellowstone. I had a bivi sack and would sleap on the sides of roads and trails. I remember walking past Gardner. Twards the end of that town there is a hotel that had a sign that informed me of their great spa, cable and rec room or whatever. I passed it and continued to walk into the Montanan nothingness with nothing to think about except that damn hotel, I turned around about 3 miles out and hitchhiked back into town and stayed the night. Best Hotel I ever stayed at.
Edit
I dont know how long the walk was or how long it took me.
When I did a lot of volksmarches, 6 miles was a reasonable distance. The longest volksmarch I did was 12 miles, which seemed ridiculous at the time, but isn’t really that far in absolute terms.
The very longest walk? About a mile with bleeding blisters on my feet.
Never take a long walk in brand-new shoes… :smack:
I ran a marathon one time, which I’m pretty sure is the farthest I’ve gone only on foot.
For walking, though, I don’t know what it would be. I regular take 4-5 mile walks, and after getting drunk with a mate the other night, I walked a cool 7 miles through hill and dale to make it to waffle house. Round trip puts me at about 14 miles. It wasn’t too bad, but I did end up with a wicked case of poison ivy swelling one of my eyes shut and minus one iPod which fell out while scaling a fence to run across the highway. Ha!
The most 28-30 miles in a day. The hardest, twenty miles. About 13 uphill, 7 down. It was harsh. both uphill and down. It was in the boy scouts.
I walked around the headland of Cornwall a few months ago. It took about 4 days to go from Penzance to St Ives along the South West Coast Path. The path was very muddy and nasty in many places, after what the locals called “the worst summer in a hundred years”.
Not counting, down the Aisle to get married? 
Probably about 15 miles or so. And that was in batches of 5 miles at a time, with a little rest here and there.
I could never do that now, sadly.
About 40 miles during a 4 day hike, so nothing all that bad. Of course, we were only making about 2 miles an hour, less in some cases, because the course we took was pretty rough. We didn’t take a regular trail.
I walked home after getting stumbling puking drunk one night when I was in college, and my ride home fell through. That was about 10 miles or more. Took me 3 hours and a bit. I was pretty sober by then 
I try to get two or three week-long hikes every summer, 7 to 10 hours of walking each day. My longest walk in one day is 46 km (28 miles or so). IIRC, it was about 11 hours including stops. There are some hills on that route, but mostly it’s flat terrain.
I don’t carry much food on these trips; there are a lot of staffed lodges and self-service cabins in the mountains here in Norway, so that keeps the weight of my backpack down.
Well, I can’t really tell how much it totalled, but for the two weeks of high school summer camp, the regime was:
The “pool” was a widening in a river on the next valley over, 7km away and over some mountains. So on a “rest day” we walked 28km, on a normal day more.
Maybe 10 miles in a single day.