What are the Seven Second Summits?

The second-highest mountain on each continent:

• K2 in Asia (8,611 m28,251 ft)
• Ojos del Salado in South America (6,893 m22,615 ft)
• Mount Logan in North America (5,959 m19,551 ft)
• Dykh-Tau in Europe (5,205 m17,077 ft)
• Mount Kenya in Africa (5,199 m17,057 ft)
• Mount Tyree in Antarctica (4,852 m15,919 ft)
• in Oceania either Puncak Mandala (4,760 m15,617 ft) on the Carstensz list or Mount Townsend (2,209 m7,247 ft) on the Kosciuszko list.

Harder than the 7 summits?

As a set, yes. By their normal routes K2, Mount Kenya, Dykh-Tau and Mount Tyree are harder than the highest peak on their continent, Ojos del Salado and Mount Logan are about the same, and Mount Townsend is a short walk. K2 alone has a death rate far above Everest's, and Tyree is the hardest of the set to reach. That is why only a handful of people have climbed all seven.

Who climbed them first

Christian Stangl of Austria is recorded as the first to complete the Seven Second Summits, confirmed by Guinness World Records in 2013. Hans Kammerlander's earlier claim did not stand, after doubts over his Mount Logan ascent.

Each peak, and how it compares with its taller neighbour, is in Why is K2 not one of the 7 summits, and are the second-highest mountains harder?