So, most people hopefully know that (sadly) north and south Korea are technically still at war and just have a long lasting cease-fire that north korea has nonetheless violated a view times already. For good measure they've also dug some long tunnels under the border between the 2 countries (aka DMZ), and at least 4 have been found, but more are expected to exist.
The surprising thing is that you can easily visit the South Korean side of the DMZ, but even more surprising, you can visit the JSA on most days. The Joint Security Area is a shared piece of land between North and South Korea where both can meet, and it was also used in the past to exchange prisoners of war (kind of amusingly so, a lot of north korean POW asked not to be sent back to North Korea, which made North Korea kind of upset and delayed the cease fire back in the day).

We did a tour that started with the DMZ, which includes seeing the 3rd tunnel the north koreans were planning on using to invade one day, a (too quick) tour of the observation point where you can look at north korea through binoculars, but sadly you aren't allowed to use cameras from the place where you could actually get decent pictures, which was most disappointing. Whatever few shots I took were quickly stopped. Apparently it's not like the South Koreans really care, but they have a deal with the North Koreans to not allow those pictures:

entrance to the DMZ area and passport check

entrance to 3rd tunnel

it's really just a long tunnel that gets low enough in places that it's quite uncomfortable if you're my height (1m77)

apparently there are still real mines left in there

the DMZ is the no man's land area between the 2 yellow lines, with the border in red in the middle

the observatory

you're allowed to take selfies, but not to take pictures without yourself in that area

Last, but not least, they took us to a train station (Dorasan) that was supposed to unify south and north korea by allowing trains from south korea to transit through north korea to china, Russia, and Europe. Sadly, after the deal was made and the station built, both the north and south korean leaders died of old age and the north korean one was replaced by the crazy kid currently running the country, who then promptly denied train passage through north korea. So they now have this nice pristine totally unused train station, even with customs, that's just gathering dust. Pretty sad, really...

never ever used customs room

The tour was over for most people by then, but we had signed up for the JSA portion of the tour too. To be honest, I'm not sure how worth it the DMZ only tour is. You get to walk in an uncomfortable tunnel for a while, you then go to an observatory where you are not allowed to take the pictures you'd like to take, and then you see a train station that sadly was never used for its intended purpose. The JSA (Joint Security Area) part of the tour takes you further in to the actual border of North and South Korea, where they meet on occasion, and where they have exchanged prisoners in the past.
To get there, you become a guest of the United Nations, get on a UN bus with a US Army escort, and you get to see the freedom house, as well as the conference room that's right on the line between the 2 countries and where you can technically step on north korean soil for a few minutes. How cool or important to do, that is, it's for each to decide, but Jennifer did remark that it's a lot of bussing around and safety checks for the time spent there. Also, you're not supposed to take pictures in most places there, although a few were ok. Interestingly they allowed us to photograph North Korea from there, but asked us not to photograph South Korea behind us:

the south korean soldiers stand there all day with their fists clenched starting at the opponent (a single poor north korean guy with no so good looking clothes) on the other side

I actually feel sorry for the guy, he looks more scared than mean

I assume they are short on staff but are watching back nonetheless :)

the joint conference room

to be honest, I'm not sure the South Koreans who stay there many hours without moving at all, are having a great time either

So, that's that for the DMZ+JSA. Is it worth doing? I'm not certain, I guess each should decide. I should add however, that having been to the excellent War Museum in Seoul, we already knew all the details about the conflict and current situation, so that's not something we learned from the DMZ tour, but for someone who doesn't know, it would be more interesting.