Glacier National Park is located in St. Mary, Montana...the northwest corner of the state, close to Canada. The Waterton Lakes Nation Park of Canada is actually the other side of the Lewiston Mountain Range. The elevation starts low and ends up with commanding views.
Pro Tip: The Going-To-The-Sun Road is a popular route through the park. It's closed seasonally and requires reservations. Plan early and get access through recreation.gov. Also, elevation is taxing. Know your limits and bring lots of water.
