1. They climb up the hill to the tower of London.
2. He is climbing up the ladder.
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Is 'up' an adverb or a preposition?
In both of these sentences, "up" is used as a preposition. The phrases "up the ladder" and "up the hill" show that it's a preposition.
However, "up" is used as an adverb in this sentence.
Joe looked up at the tower.