In spite of is name, the steam railway actually runs from Kingswear (across the river from Dartmouth) to Paignton. The route runs upriver along the Dart, then swings across through Galmpton, then along the coast from Goodrington into the heart of Torbay. Apart from the views and the delights of Paignton itself, one attraction (especially for kids) along the way is the Quay West Water Park, next to Goodrington Station (in the background below).
The railway journey forms one side of the triangular ‘Round Robin’ trip, which allows customers to ride from Paignton to Totnes by bus (open topped if required), then by boat from Totnes, back down the river to Dartmouth. Of course, you might like to do it the other way around, but check times for the boat, as the river looks at its best when the tide is high. You will need to buy a ticket for the passenger ferry across to Kingswear too.
If you really want to overdose on steam, you can also take a trip from Totnes to Buckfastleigh and back along the river Dart to the edge of Dartmoor – see the South Devon Railway website.