For bikers Ranong Canyon is a fine morning excursion. You'll of enoyed the challenge of the Highways roads but this will make for interesting challenge all on its own.
Firstly take the Springs turn-off and follow the road past the Hot Springs. It'll narrow and soon you'll be looking at the terrain in the top picture.
The road is narrow and makes for some nice bends and corners.
You'll pass through a small village with signs for a temple on your left. Keep going and follow the road around. At the T-Junction turn right. This road will take you through the remainder of the canyon.
You'll pass by on your right what could be described as a lake taken straight from the Garden of Eden. Flanked on one side by rocky crags it sets a nice tone for the journey.
Some refreshments are available nearby.
As you keep going you'll pass a small hamlet where all the road edges are littered with nuts!
Once past the Hamlet the road narrows again and soon it ends and becomes a trail. There doesn't look to be much worth exploring past here...
Map of Ranong
Being about 420 km from Bangkok means about 4.5 to 7 hours drive time. A distant airport operates flights out of the city but this is usually on an infrequent basis.