From Bohinjska Bistrica we bike by the main road towards Bled, but only about 1 km.
In Bitnje (south of the village there's a cute cemetery church, worth visiting) we deter left, on the road towards Pokljuka plateau. It ascends steeply, first with some view down in the valley, then through a quite narrow gorge. The road exits the gorge near Jereka village. We are now in the Upper Bohinj Valley.
From Jereka, nice, sunny villages continue up towards Pokljuka, but there we deter immediately left - down towards the Bohinj Lake. The road is nice and open, we descend quickly.
Srednja vas is the first village worth of exploring it a bit. We ride through it, the church is right above the road. On the village exit, we deter right from the main road and ride into Studor village.
Typica Bohinj architecture of peasant houses continues in Studor. Especially interesting is Oplenova hiša, an old house which is nowadays arranged into an etnologic museum. From the village center we best keep left, hitting the main road again. But before reaching the main road, we ride past a group of famous double hay-racks (called "toplar"), a real etnological landmark of Bohinj.
Then the main road leads us directly to Stara Fužina. That's a bigger village, known by the iron works of Zois family, from more than two centuries ago.
Even if we could proceed by the main road directly to the lake, here I'm suggesting to visit also the Devil Bridge. It's one of many bridges in the Alps, for which a legend says it was built with a help of Devil, who claimed in return the soul of the first being who will cross the bridge upon completion. Locals in Bohinj were crossing over the Devil by pushing a dog over the completed bridge.
So, we keep in Fužina right and detour the village by the northern side. From the bridge, the view down into the narrow canyon is spectacular! On the other side of the bridge, we do some more ascent and finally reach the road, which leads into Voje valley. There we turn left again, starting the descend to the lake.
We ride down to Fužina village again. To the lake we can ride by the main road, but if possible, try to find the first possible shortcut to the right (even if walking a bit). The eastern shore of Bohinj Lake is really beautiful!
Along the lake shore we bike towards the cult place where Sava river flows out of the lake. There's the nice, old bridge and next to it the famous church of Sv. Janez - the post card motif of all tourist ads of Bohinj.
From the bridge, we could return to Bohinjska Bistrica by the main road. But that't trivial and the road is busy. Yes, do ride in Ribčev Laz only to the monument to the Four Brave Men - the locals who first climbed Mont Triglav (even before Mont Blanc was climbed). But then turn around and cross the bridge again back towards the north. Ride towards Stara Fužina, but only till the first bridge on the right (over Mostnica river). There the nice biking track starts. It will lead us all the time along the left bank of Sava river. Nice stretch of a biking trail, pure nature, almost no people there.
When approaching Bohinjska Bistrica, you can consider crossing Sava river before the village (after Brod village). If you don't, then in Bistrica you'll need to ride a short stretch of the trail back.