Edgar Rice Burroughs 
Carson of Venus 
Venus Book 3

Carson Napier, first Earthman to reach Venus, had to keep alert every instant of his stay on that world of mist and mystery. For its lands were unmapped, its inhabitants many, varied, and strange, and he had taken an obligation to restore a native princess to her lost homeland. On terrible oceans where dreaded sea-monsters dwelled, in deep forests where terror haunted every branch, and behind the walls of eerie cities where power-mad chieftains plotted uncanny schemes, "Carson of Venus" is fast-paced science fiction adventure.