Water locked underneath icecaps or glaciers can tell us about our planet's past and its possibly warmer future. Similar environments on distant worlds could tell us whether life can originate in these harsh conditions. To study the icy depths, a Swedish team of researchers is designing a tiny submersible that can slip down a narrow borehole. There exists a menagerie of different remotely operated underwater vehicles (ROVs), some of which have already studied the frigid boundaries between ice and sea. However, none of them are compact enough to snake their way several kilometres below the ice.