Belcher Glacial Tunnel, Devon Island, Nunavut, Canada

This is an enormous ice cave within a glacier. It was formed by the flow of meltwater deep inside the glacier. The phenomenon is also known as an englacial melt channel.

Covering 55,000 square kilometres — about the area of Croatia — Devon Island is the largest uninhabited island on earth. It is home to a handful of musk-oxen and a few lemmings, but no humans live there year round. 

A third of it is covered by an ice cap. Lying at 77 degrees North latitude, it has fewer than two months of snow-free days per year.

Image by Alex Gardner