This is a glacier ice cave that is actually now an iceberg that has broke off of the Mendenhall Glacier. It floated about a hundred yards from the glacier and is now frozen into the Mendenhall lake for the winter. The frozen lake water provides a flat floor to the room. The ceiling at the highest point is about 30 and the overall length of the tunnel is about 100 feet. It was created by an under glacier river which use to flow through here and is now weathered away from the main glacier.