[i] "Hurry up!" their mother said, and the three boys clambered onto the train. . . .
[ii] They were carried along a dark tunnel, which seemed to be taking them right underneath the castle, until they reached a kind of underground harbor, where they clambered out onto rocks and pebbles. . . .
[iii] Then they clambered up a passageway in the rock after Hagrid's lamp, coming out at last onto smooth, damp grass right in the shadow of the castle.
(Harry Potter and the Sorcerer's Stone)
Does this word, clamber, used only when somebody climbs up something using their hands? Or can it also be used when they don’t use their hands?