You can approach the Galilee from the southeast on the road that runs northward up the Jordan Valley, or there are two good central routes for entering Galilee from the west: One is from Haifa to Akko and east to Safed, then down to the Sea of Galilee. The other is due east from Haifa to Nazareth and straight across to Tiberias. An offshoot of the Haifa-Nazareth road is a route that detours down through the Jordan Valley, south of the Sea of Galilee; at the Jordan Valley, turn north. In summer, the Jordan Valley, which is far below sea level, can be oppressively hot. Give yourself time to enjoy the beaches of the Sea of Galilee, which can be paradisiacal.
The Galilee is filled with so many places of natural and historical beauty that it's worth it to rent a car, at least for a few days of travel.