In the village of Bustelo, in the municipality of Coristanco, we will leave the car after passing some greenhouses. From here we will go down to the river and the watermills. The O Grelo river rises near the village of Bustelo. It is fed by the Martín stream on the left and the Fontes stream on the right. It flows into the Calvar river, a tributary of the Anllóns river. The route is not signposted.