We visited Mt. Cook as part of the land tour of Australia and New Zealand.  Mt. Cook is located in approximately the middle of the south Island and the views were spectacular.  We had clear weather, which we were told can be a bit of a rarity.  I hiked for about 30 minutes from our hotel, which was located right in the park area to a viewing platform to get the best views.   This was well worth it.   The hotel had a decent sized museum dedicated to Sir Edmund Hillary, a famous explorer from New Zealand.