Tombs

There are tombs and pagodas everywhere in and around Hue. Those with an endless appetite for culture can sate themselves every day for a solid week, and there will still be more left on the table. But the majority of travellers we run across are satisfied with just a taste.
As regards the tombs, there are a couple of important things to remember. They are not particularly old -- they were built within the past two-hundred years. This makes it even more surprising that most of them are already falling to pieces. This is partly due to poor upkeep over the years, and partly due the original construction techniques, which weren't all that exceptional.
The tombs were built by puppet emperors who had little real power, other than to sit around contemplating their own deaths and building monuments in anticipation of the occasion. Like Graceland, Never Land, and Sam Simeon, they are monuments to ego, but in this case, the egos involved are much more obscure and less interesting to contemporary visitors.
That said, some of the tombs are located on large, beautiful grounds, and the crumbling edifices exude a certain air of aesthetically-pleasing decrepitude.
Tu Duc is on the most expansive grounds, and takes the most time to see. It's rivalled by Ming Mang, which is also on a large plot, but we thought Tu Duc was a little better. Choose between the two so you don't suffer from tomb burnout, but then definitely see Khai Dinh -- it's in a different style from the others, is smaller, easier to visit, and in better shape. Gia Long is, by far, the best adventure in terms of a visit, it's usually deserted, and the ethereal natural beauty of the spot is hard to beat.
Tu Duc, Khai Dinh and Minh Mang have a 55,000VND admission and are open 08:00-17:00. Gia Long is free and open all the time.

Getting There

Tu Duc
From Le Loi head south on Dien Bien Phu (across from La Residence), for 2km until it ends at Nam Giao. Take a right on Le Ngu Cat, go 2.2km to where it tees with Nguyen Tran Cong Chua. Take a left, the tomb is 700 metres down, on the left.

Khai Dinh
From Le Loi head south on Dien Bien Phu (across from La Residence), for 2km until it ends at Nam Giao. Jog right then immediately left, heading south on Minh Mang. The tomb is 5km down on the right.

Minh Mang
From Le Loi head south on Dien Bien Phu (across from La Residence), for 2km until it ends at Nam Giao. Jog right then immediately left, heading south on Minh Mang. Five km down you'll pass Khai Dinh Tomb on the right. Continue 1.3km, to where a short right turn leads on to the main highway. Take a left on the highway (northbound) 1km to the turn for Minh Mang on the left -- look for the roadside cafes and a blue sign. After turning left go straight, 2km, to where there's a left turn at the base of a hill -- more cafes mark the spot, but no sign. Take that left, the tomb is 800 metres down.

Gia Long Tomb
From Le Loi head south on Dien Bien Phu (across from La Residence), for 2km until it ends at Nam Giao. Jog right then immediately left, heading south on Minh Mang. Five km down you'll pass Khai Dinh Tomb on the right. Continue 1.6km to where the road ends at the river. Take a left, and the first boat landing is about a kilometre down the road. You'll need to catch a boat across to see the tomb. There are several more boat landings further down the road, but the road gets progressively rougher.