A Wisconsin Public Radio report says the ice is solid, although you might be able to feel it moving on the water below it.
Apostle Islands National Lakeshore superintendent Bob Krumanaker says the experience of walking on a frozen Great Lake is remarkable, both physically and psychologically.
The mainland caves are 18 miles west of Bayfield. With the current conditions, the National Park Service says the caves are a "fairyland of needle-like icicles."
Krumanaker says there are beautiful rock formations covered by icy stalactites and stalagmites. He says if you crawl under them, the ice is like a glass floor through which you can see the bottom of the lake.