What word best completes the sentence: Harry was just comparing this hotel with the one _____ he stayed in during his trip to Norway?

The correct choice is "where" because it appropriately indicates a location or place. In the context of the sentence, Harry is comparing a hotel to another hotel he stayed in previously. The word "where" directly refers to the location of that hotel, making it clear which hotel he is discussing in relation to the current hotel.

Using "how" wouldn't work in this context, as it refers to the manner or way something is done rather than a place. "What" is also unsuitable, as it suggests an object or thing, which does not fit the need for a location in this sentence. "When" indicates a time, which is irrelevant to the comparison of hotels. Thus, "where" is the most logical and grammatically correct choice for completing the sentence.