Seaton to Seaton Junction
Seaton Junction to Exeter Central
Exeter Central to Barnstaple and Instow
Unfortunately, your chubby blogger does not have a suitable rail timetable, so cannot work out how long it would have taken. (Any offers out there?) By car the single journey took 1 hour and 45 minutes!
There may not be much working railway beyond Barnstaple, but there is certainly plenty to explore. Still to be researched, Barnstaple to Ilfracombe and Bideford to Westward Ho! and Appledore.