Icicles glisten as throngs of visitors explore frozen sea caves, seen in the above February 14 picture.
"Personal sled dog trips can be made to the caves. Commercial sled dog trips are not allowed," the park notes, and horses are forbidden as well.
This is not your typical beach trip. Frozen lake ice opens a bridge to visitors, shown here tromping away on their visit on February 15.
Cave visitors take a cold walk of three miles or more over the ice to explore cliffside sea caves draped in the mantle of winter. The ice caves haven't been accessible on foot since 2009, and the park reports throngs of visitors this winter, especially on weekends.
Watch out where you walk in the ice caves. Here sightseers duck to dodge small icicles hanging from a cave roof, shown in this February 14 picture.
The caves formed from the action of lake waves on ancient sandstone cliffs that ring the park. In the summer, crashing waves make them inaccessible to visitors.
For now, the park's website warns folks that some of the bigger icicles weigh hundreds of pounds and might pose a threat: "There are large icicles and frozen waterfalls suspended from the top of the cliffs," says a park statement. "They might break off and come crashing down at the most inopportune moment."
Winter splashes hoarfrost on the ceiling of the ice caves. The needles form when moisture in the air condenses and freezes.
The pink shades of the longer icicles arise from the cave's red sandstone. Ruddy sand grains slough off the cave walls as the icicles grow.
Jeff Neddo of Eagle River, Wisconsin, tightens the crampons on his snow boots as he gets ready to visit the ice caves.
Spike footwear is always in fashion when visiting the ice caves. The park recommends: "The areas along the caves tend to be very icy. There is a well-worn path, but it is uneven—a ski pole for balance may be helpful."
A sled for pulling the kids might also help.
Surf's up! Frozen foam sprays from the roof of an ice cave, observed by Mike Rundle of Janesville, Wisconsin, in this February 15 picture.
Even in the heart of winter, lake ice is never guaranteed safe for travel. A trip on the lake ice comes with warnings, such as the one shown in this February 15 picture.
Even the dog packs a sweater on the trip to the ice caves. Both suitably dressed, Pete Miller of Minong, Wisconsin, and his dog Max peer through a cave opening.
A wintry mantle hangs from the sea cliff walls at the Apostle Islands National Lakeshore, seen in this February 14 picture. The base of the ice wall glows pink because of red sandstone scraped from the cliffs.
Sunset shines on the icicles adorning the cliffs at the Apostle Islands National Lakeshore, accentuating the sandstone entombed by winter.
Some 88 percent of the Great Lakes are covered with ice this winter, a silver lining for ice-skaters and ice fishermen in a severe winter.