I swam across the Rio Grande from Texas to Mexico and back at the Langford Hot Springs near Big Bend. That was a swift current! Luckily I’m a strong swimmer.
Israel/Lebanon.
Within the US, I’ve crossed DC-MD, and KY-TN along the Appalachian Trail.
I’ve crossed from the US to Canada on foot on the Niagara Falls bridge, and from the US to Mexico at the border crossing between El Paso and Ciudad Juarez. I also crossed between Mexico and Guatemala on foot at a border crossing.
I’ve also hiked a trail that runs along the Panama-Costa Rica border, and crossed the border multiple times.
Vietnam -> Cambodia. Was on a bus traveling from Ho Chi Minh City to Phnom Penh, a five-hour trip (I think), but the bus let us off a few hundred feet before the actual border for passport control, then picked us up just on the other side of the line.
New York <-> New Jersey, a bunch of times. Mostly by walking over the Geoge Washington Bridge, but a couple of times while hiking as well.
Maine -> New Hampshire, on a kayaking trip on the river that forms part of the border between the two states.
I currently live on an island in the Columbia River, which serves as the Oregon-Washington border. Technically, I live in Oregon, but if I want to go to the mainland by foot (I don’t own a car) it’s easier to go north to Washington. I walk over to Vancouver, WA regularly. If I want to go see Portland, I take the bus.
Other than that, I got nothing.
None though I could change that pretty easily. I live within walking distance from the CT border but I have no reason to go that way so I never bothered.
Australia
NSW-Qld both walking and swimming
Vic-NSW at several points on foot, swimming and rafting
Vic-SA on foot
NSW-SA on foot
I’ve walked across the U.S. -Canada border at Niagara Falls a number of times.
I walked across the Israel-Jordan border–we took a tour bus to near the border, and hauled our posessions for half a mile to the next tour bus (with border crossing paperwork in the middle).
I’ve been to the Four Corners in the U.S., and have been to many U.S. States, but if I’ve walked across any other state borders, it wasn’t all that memorable.
Kansas to Missouri, and back. All I had to do was walk across the street.
I’ve done MD-DC a lot since I work right at the line. I’ve also done the Cumberland Gap so I guess KY-VA. I also swam across the Potomac once, near the mouth, so VA-MD the hard way. There might be others, but off the top of my head I can’t think of them.
CA/NV at South Lake Tahoe/Stateline, on a number of occasions.
Italy/Vatican City, as has been mentioned above.
TN-VA in Bristol
KY-VA at Cumberland Gap
TN-GA just outside of Chattanooga
TN-VA hiking on a trail between Hancock County, TN and Wise County, VA
TN-KY at a festival just north of Portland, TN
IN-MI up around White Pigeon
US-Mexico crossing at Laredo
CO-UT-AZ-NM at the four corners
TX-AR in Texarkana
IN-IL around Calumet City
Every other crossing has involved trains, planes or automobiles.
I’ve crossed the GA-TN border by whitewater raft on the Ocoee River. Also, I presently live on the Clearwater, Fl - Dunedin, Fl line and I walk across it every morning to get the newspaper.
NV-CA at Lake Tahoe and NV-AZ at Hoover Dam and according to my father I have crossed from VT-Quebec border on foot. (Illegally?) There is a golf course in Northern VT and my Dad is positive that part of the course is actually in Canada. Google Earth tells me it is close, but I think everything is in the USA. The closest it gets to Canada is about 100 yds.
Once into Mexico from the US at El Paso.
Once between Ontario and Quebec at Ottawa.
Several times into Tijuana from the US. It was that or take a car, totally not worth the hassle.
Several times betwen Arizona / Nevada at Hoover Dam.
Several times between Nevada and California at Lake Tahoe.
My very first venture off of US soil was walking into Juarez, Mexico from El Paso, Texas in the wee hours one morning long ago. Since then, I have also walked across the border between Tijuana, Mexico and San Diego, California.
There’s also Laos/Thailand and Cambodia/Thailand. Maybe Malaysia/Thailand; we took the train, but IIRC we had to exit the train, deal with Thai Immigration and Customs, then walk to the Malaysian side and deal with their Immigration and Customs, then reboard the train over there.
United States to Mexico, or Texas to Chihuahua, via the Paso del Norte bridge from El Paso to Juarez.
Four Corners: New Mexico/Arizona/Colorado/Utah. Jumped across to make all the border crossing combinations.
Colorado to Kansas: US 36, stood in Colorado, peed into Kansas.
Among U.S. state borders, the border at South Lake Tahoe. I checked into the easternmost California motel and walked to gamble.
Among international borders, I’ve walked from Thailand to each of its neighbors, as that is (almost) a requirement of border control.
"Oh yeah, the partial building remains right on the river down from Rio Grande Village? Forgot about that one.
"
That’s it.
Just remembered… Greece > Turkey. Turkey BP had us get out had us walk across as they searched our bus and hassled our guide. Man, those two countries have a lot of animosity toward each other.
Me too! On the Appalachian Trail.
Also:
MD to DE and back at the same place as lukeinva.
MD to VA and back on Assateague Island
DC to MD on the C & O Canal towpath