To climb with some difficulty, or in a haphazard fashion.
The children clambered over the jungle gym with reckless abandon.
Tennyson
The narrow street that clambered toward the mill.
1898, (w), (w) Chapter 4
Thus, sitting where I was, I lit my candle once more, and then clambered across that great coffin which, for two hours or more, had been a mid-wall of partition between me and danger. But to get out of the niche was harder than to get in; for now that I had a candle to light me, I saw that the coffin, though sound enough to outer view, was wormed through and through, and little better than a rotten shell. So it was that I had some ado to get over it, not daring either to kneel upon it or to bring much weight to bear with my hand, lest it should go through.
1912: (w), (w), Chapter 6
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.