The western end of the Greek National Road 20 is in the centre of Ioannina, where it is connected with the national roads GR-5, GR-6 and GR-17. It runs northwest towards Kalpaki (junction with GR-22), where it turns northeast towards Konitsa. Between Konitsa and Tsotyli it passes through the Pindus mountains. The section between Neapoli and Siatista is shared with the GR-15. From Siatista the GR-20 continues east, until it reaches the city Kozani, its eastern terminus.
The Greek National Road 20 passes through the following places (west to east):