Maybe there is more here than you would think. Dartmouth is a steeply sloping town on the West side of the Dart and there are actually two car ferries across as well as one passenger ferry to Kingswear, a similarly steep town on the other bank. There is a steam railway which I have never actually used from Kingswear to Paignton, where the station is very close to the main line.
To many Dartmouth means the Britannia Royal Naval College and tis does rather dominate the upper town. Guided tours of the college are possible. However, there is much more than this. The principal historic treasure is the Newcomen Engine. This one was built at the end of the 18th century but there were over 100 in use at the time of Newcomen's death in 1729 and the first scale model for this type of steam engine was made as early as 1710.
Another interesting historical building is Dartmouth Castle, about a mile from the town and open to the public (Kingswear Castle is not).
The Butterwalk, covered but open at the front is well over 300 years old and there are veyr interesting old streets in Foss Street and Browns Hill. lastly, coming back to the water, the town should be of interest to students of American history as the Mayflower and the Speedwell left here in 1620.
So much for the town. There are river trips in summer between Dartmouth and the old inland borough of Totnes and this is one of the most picturesque estuaries in England. People who have owned land or buildings beside the river include Sir Walter Raleigh and Dame Agatha Christie and pretty villages include Dittisham and Stoke Gabriel.