IIRC, there's a tidal road on the western side of the river at Aveton Gifford - might get lucky and find someone stranded on it...
Depending on how much time you have spare, there's all of Dartmoor to explore. Plymouth Marine Aquarium is worth a visit, as is Dartmoor Zoological Park a few miles East of Plymouth. Cap'n Jasper's hut on the Barbican does great burgers - take an appetite!!!