One of the toughest things I think I have ever done. We left at 3am to get to the summit in time for the sunrise. Our base camp was at 2600m and the summit is at 3700m. We estimated it to be around -5 degrees celcius in the icy wind. My fingers stopped working while I was taking these pictures. Way below in the middle of the lake you can see the very much alive Gunung Baru or new mountain which has been spilling lava into the Lake Anak Segara for the last 16 years. This trek was definitely not easy with us having to walk for approximately 10 hours a day up and down very steep slopes.
Read about the trek here