He would clamber about the roof and windows for hours attempting to discover means of ingress, but to the door he paid little attention, for this was apparently as solid as the walls.
If you clamber somewhere, you climb there with difficulty, usually using your hands as well as your feet. They clambered up the stone walls of a steeply terraced olive grove = scramble. to climb or move slowly somewhere, using your hands and feet because it is difficult or steep clamber over/across etc (Perhaps from clamb, old past tense of climb)