I walked from Hawaii to the U.K., which is strictly verboten, and not by the Laws of Physics, as one might expect (you’re not supposed to hop over the two-foot high single link chain).
Only odd border crossing I’ve ever done was the North Carolina / South Carolina border in the middle of a theme park (Carowinds, just south of Charlotte). There’s a 2-brick-wide line of bricks through the park along the actual border.
One thing I’d like to do sometime, though, is drive to France (I live in the US).
I’ve often been to the Pheasant Lane Mall in Nashua, NH (where there are no sales taxes), but with most of its parking lot in Tyngsboro, MA (where there very much are sales taxes). One small corner of the mall was built across the state line, but when Massachusetts ruled that was enough to let them claim sales taxes for the whole mall, it was actually cut off the building.
I’ve crossed between the US and Canada by boat in four different places, now that I think of it: The (former) Scotia Prince cruise ferry between Portland, ME and Yarmouth, NS, tour boats in the Thousand Islands (NY and ON) and in Waterton Lakes (AB and MT), and on a cruise ship down the Alaska panhandle to Vancouver.
And, according to legend, when you visit the UN in New York, you are* technically outside the United States *(gasp!). Done that too.
We were going to cross from Uganda into Congo at the Bwindi National Forest, but the guys with the AKs kind of put a damper on the idea. You can do it if you’re just trekking after gorillas in the jungle, but if you’re in a vehicle it’s a good way to get shot. I don’t know WTF our driver was thinking.
The summer after 9th grade, I went on a 50 mile hiking/canoeing trip in northern Minnesota. We would paddle these little lakes, then carry the canoes to the next lake. On many of these lakes, Canada was on the northern shore. I set foot on Canadian soil many times on that trip in places where it’s possible another human foot had never been.
I hiked from Alaska to BC on the Chilcoot Trail. So I crossed the border on foot, at the Chilcoot Pass … luckily the RCMP didn’t insist that I bring a ton of provisions with me.
I visited Germany in 1992 and found it very weird to cross from Germany & France with no border control. Still early in EU days and all the border crossing buildings were still there. Similarly the trip to Berlin involved driving past very scary looking guard towers and fences that were in the process of being removed. In Berlin itself I walked along no-mans land following the sawed off posts marking the edge of no-mans land. So that would be NOT crossing unusual borders!
I remember one time crossing the Austrian-Czech border on a train during the Cold War. First we stopped on the Austrian side, and that country’s Immigration officials came through and checked everyone’s passport. Then the train inched across the border and stopped on the Czech side. We underwent a very thorough search. All passengers had to leave the train compartment but remained on the train in the aisle. Behind the seats were searched. The outside roof of the train was searched. Soldiers were underneath the train searching. We all underwent a mini interview about why we were going to Czechoslovakia. Cameras were registered, and officials checked to make sure you still had your camera when you left the country. (There was a big black-market trade in cameras in those days. I think I recall they entered the camera information in your passport, as this was pre-Internet and -computer-system days.)
And while all of this was going on, the passengers were in the aisle looking out the windows. Next to me stood a pretty girl. Suddenly a Czech soldier standing outside approached our car, and with a flourish a flower appeared in his hand. He handed the flower up to the girl next to me, and we all applauded.
No truly unusual ones for me.
Last winter on a tour in Costa Rica, I was in a boat on the Rio Frio, and we floated up to the border with Nicaragua. I stuck my hand across the crude barbed wire fence and touched a plant in Nicaragua just so I could say I’d been there. Then, our boat actually crossed the border and hung out in Nicaragua for about a minute before we returned to Costa Rica.
A couple other oddities: driving from Gainesville, Florida to Illinois, I would cross the Georgia-Tennessee border on I-75 near Chattanooga. Then I’d transfer to I-24. A few miles later, it dips back into Georgia for about 2 miles before returning to Tennessee again. All of this excitement happens only a few miles from the northeast corner of Alabama to boot!
I’ve also driven through the part of Maryland that’s barely more than one mile wide, nearly pinched off between Pennsylvania and West Virginia. Somehow they managed to fit an interstate interchange (I-70 and I-68) in that tiny sliver.
It was at a birding lodge called Cana, a former mining camp. I’ve been there about 5 times. It was considered safe the times I’ve been there, but has been closed for the past several years after a small FARC patrol came through and stole supplies.
I’ve been to the Darien about 30 times. Most of it is safe enough, but a couple times I’ve been into areas where there was potential danger from Colombian guerrillas, narcotraficantes, or maleantes (bad guys).