Exploringthenorth.com/bigspring/spring.HTML
Nowhere near as big, but certainly interesting, and much simpler to get to (though it is still quite a trip)
Kitch-iti-kipi, in the upper peninsula of Michigan.
I was by there more than 40 years ago but did not know about it. So many things to see here at home and Canada.
Ive been all over the world already. Lots id like to see but the wife does not like to travel.