Mammoth Caves, Burgess Falls and Cummins Falls
 

We are planning trip to Tennessee and Kentucky at the end of September - beginning of October. One of our target is Mammoth Caves. In this time they do not have Historic tour. They have frozen Niagara tour, Domes & Dripstones Tour, Onyx tour and Grand Avenue. At first we looked on Grand Avenue but later we read that this tour is really 'Very strenuous' . We are in earlier 60's, I'm in very good shape but my wife has had ACL surgery on the knee 14 years ago and she is afrading that there are too many stairs (700) and it's 4 miles. Is it really difficult tour? And what's about rest of tours?

Another question is regarding Burgess Falls and Cummins Falls, any tips and recommendations are very welcome. Thanks.