King Solomon's Mines by H. Rider Haggard
Allan Quartermain had been a trader and hunter all his life and knew Africa as well as any white man. He was returning to Natal, South Africa, when Sir Henry Curtis tracked him down and made him a proposition. Curtis's brother had heard of the famous, fabled diamond mines of King Solomon. He has taken an expedition into the unchartered interior to find it. He has not returned.
Quartermain possesses an old map purporting to show the way to the fabled mines so, in return for a share of the treasure or a handsome stipend for his son if he dies in the attempt, Quartermain agrees to mount a rescue expedition. They journey over snowy mountains, through deserts, and into battle, but it is when the adventurers reach their destination that they must face Gagaoola, evil, clever and the greatest danger of all.