Uunartoq is a small island about 70km southwest of Qaqortoq with a remarkable natural gift: hot springs that maintain a temperature warm enough for bathing throughout the year. Several pools have been developed with simple wooden boardwalks and changing facilities, and the experience of soaking in 38°C water while icebergs drift past in the surrounding fjord is genuinely one of the most otherworldly things you can do in Greenland.
The island is reached by boat from Qaqortoq, and most tour operators offer day trips in summer. The journey itself is scenic, passing through fjord scenery of considerable drama. The island has no permanent inhabitants, no accommodation, and no facilities beyond the basic bathing infrastructure — bring a towel, warm clothes for the boat ride back, and something to eat. On a clear summer day with the midnight sun still visible at 10pm, this is one of those experiences that stays with you.