Vietnam's Demilitarized Zone, or DMZ, is the area around the former border between North and South Vietnam. Historically it was a narrow band of terrain extending from Laos to the coast, five km on either side of the Ben Hai River, roughly on the 17th parallel, north latitude.
The area saw heavy fighting in the war, and ruins of old American military bases still exist. Even if you're not interested in the history, the area has some spectacular mountain scenery and rugged jungles.
While the actual border was marked by the Ben Hai river, most historical sights (i.e., American bases) are along Highway 9, which runs parallel to the river several km to the south. This road runs to the Lao border and continues onward.
The area's only major city is Dong Ha, on the coast. It's on Hwy 1, and easily accessible from Hue and Da Nang.
Tours can be arranged from Dong Ha by DMZ Tours (located along Le Duan street) for around US$15-17. This tour will pick you up on the bus coming from Hue, and go to the tunnels, Dakrong bridge, rockpile, and Khe Sanh. Does not include Camp Carol, Con Tien, or food/water, but is a pleasant ride with a spirited guide (some propaganda).
Lots of travel agents in Hue offer convenient day trips by bus. They are cheap at US$10-15 per person, but be forewarned that you will have to get up very early, as the tours usually start at 06:00. Expect to return to Hue between 18:00-19:00. You will also be herded back on to the bus to continue to the next stop, only to find yourself waiting for some stragglers. It can get crowded in the Vinh Moc Tunnels if your bus group is large.
You can go by car, which can be expensive, but if it's raining, which it often is, you'll be glad you did. Also, private tours can take you to some places where the big buses and large groups don't.
Tours by motorbike can be arranged, but unless you are a diehard such is likely very tiring as distances for a round trip can be as high 300 km. If you want a motorbike tour, it may be better to spend a night in Dong Ha and make arrangements there.
Booking through a hotel will probably cost more due to commission.
Unless you have your own transportation, you'll need to hire a taxi or take a guided tour to see the sights. Some local tour operators offer motorcycle trips along the Ho Chi Minh Trail.
Arranged in order from east (Vietnamese coast) to west (Lao border):
Though you'll probably encounter vendors selling GI dogtags, lighters, and other paraphernalia, you can be sure that none of them are genuine.
Quang Tri is famous for pepper bean and Arabica coffee, and can be purchased in Dong Ha Market, next to the Dong Ha bridge, on Hwy 1.
You can either move to discover Phong Nha-Ke Bang or enjoy your next days in Hue city. Other than that, you can take a bus and get to Laos from Dong Ha City.