The National Park Service will open iced-over sea caves of Lake Superior, in Wisconsin, USA to the public this Saturday.
Hundreds of years of wave action has sculpted the sandstone caves with delicate arches, vaulted chambers and honeycombed passageways.
Last year was the first time the caves were open for five years, and 140,000 people made the one-and-a-half kilometre-long trek along the beach to reach the caves, which continue for almost four kilometres.
