What is the fine-grained topic of the following text: In this five-part series, climbers Nico Favresse, Olivier Favresse, Seán Villanueva and Ben Ditto ship out for the summer with Captain Bob Shepton on his 33-foot sailboat in search of unclimbed big walls rising out of Greenland’s fjords. Only return the topic.
Climbing expedition in Greenland's fjords