On all the southern routes and on the Western Breach climb it is possible to sleep overnight in the crater. This has three major advantages. First, it is possible to reach the summit during the day, avoiding the midnight rush. Second, there is time to visit the crater and explore the glaciers. Finally, it is possible to get back to the rim very early the next day to see the sunrise. The Furtwängler Glacier on Kilimanjaro is a remnant of the ice cap that once covered the mountain. This has retreated dramatically over the last century with over 80% glacial retreat. The glacier is named after Walter Furtwängler, who along with Ziegfried Koenig, were the fourth to ascend to the summit of Kilimanjaro in 1912.