Bolu is mountain country first and everything else second. Mountains cover 56 per cent of the province. The Bolu range runs south-west to north-east, topping out at 1,980 metres on Çele; the Abant mountains reach 1,748 metres; north of Gerede stand Arkut at 1,877 and the Göl mountains at 1,112. Higher than any of these, along the southern edge, are the volcanic Köroğlu mountains, which reach 2,499 metres.
Between the ranges the plains run east to west and take up 8 per cent of the province. The widest are the Bolu plain at 725 metres and the Gerede plains at 1,300; the others are Yeniçağa, Mudurnu and, south of Göynük, Himmetoğlu. The southern spurs carry their own names — Seben at 1,854 metres, Ardıç near Mudurnu at 1,443, and Çal Tepesi at 1,640.
