There was/is a companion app called PebbleNav/NavMe that worked okay-ish, as long as you could survive with "Turn left in 100 metres to x street" type instructions with no map view (not really something you can do with 144x168 pixels).

There is an Android and a companion Pebble app ("Nav me") that reads the Google maps notifications ("In 300 meters turn left onto Jefferson Street") and displays them on the watch. The remaining distance until the next navigation instruction decreases real time. Nothing fancy like minimap view, but can be useful in some situations.