It is located in the US State Park as phpr states above. I did find a Trip Advisor report from 2014 that quotes a $1 admission fee. If you drop down from Google Maps you do get this image, https://goo.gl/maps/QzZupFiYGRu showing that it is associated with the Maid of the Mist. It does give the US side a view of the Horseshoe Falls that is much better viewed from the Canadian side. I'm wondering if the elevators in the tower are how you get down to board the Maid of the Mist?