The northern part of the province is in the Sankamphaeng Range, the southern prolongation of the Dong Phaya Yen mountain range, with the highest elevation the 1,292 meter high Yod Khao Kiew. Most of that area is covered by the Khao Yai National Park. The central part of the province however is a rather flat river plain formed by the Nakhon Nayok River. The southern part of the province has relatively infertile acidic soil.
The main river of the province is the Nakhon Nayok River. It joins the Prachinburi River at Pak Nam Yothaka in Amphoe Ban Sang, Prachinburi province, which then becomes the Bang Pa Kong River.
Wang Takhrai is a botanical garden belonging to the Chumphot - Phanthip Foundation. Located at the Wang Takhrai waterfall it is a popular place for tourists to visit. Several other waterfalls within the province are well known tourist destinations: Nangrong and the nine-leveled Sarika waterfall are in Khao Yai National Park, as is the Lan Rak (or Tat Hin Kong) waterfall.