As Els says, the tombs of Hue are widely scattered, some more than 10 kms from the city centre. But they are reachable by taxi, or by boat along the Perfume River. One that I visited was the colourful tomb of Ming Mang, where you pass through several gates and temples before reaching the actual tomb on a hillside at the rear of the complex. Another was the tomb of Khai Dinh, a complex of grey stone with lots of steps and elaborate stone decorations.
While touring the district I also visited the tombs of Tu Duc and Duc Duc as well as the Thien Mu Pagoda.
Inside Hue itself the huge Citadel, a complex of many differing styles filled a large area. The memorial house in Phan Dinh Phung Street and the An Dinh Palace were much smaller, but were all within walking distance of the city centre.