Beneath the Planet of the Apes

Beneath the Planet of the Apes was the first sequel to the 1968 movie Planet of the Apes. It stars Charlton Heston (although he is in a very small supporting role) and James Fransicus (although Burt Reynolds was originally intended for this role). The military Ape General was originally supposed to be played by Orson Welles.

Warning: Wikipedia contains spoilers

The ending takes place under the planet's surface with a confrontation between an army of apes, Heston and Fransicus, and a mutated white robed people who worship "the bomb". The planet is destroyed by the atomic bomb going off via the hand of Heston.