Is camping beside Segara Anak Lake warmer and less windy than camping on the crater rim?

Lower, yes; reliably warmer, no. The arithmetic favors the lake by a wide margin on paper: Plawangan Sembalun sits at about 2,639 meters, while Segara Anak lake lies at roughly 2,010 meters, a difference of about 629 meters. Air warms as you descend, so the lake camp is generally the milder night, and it is usually less exposed to the wind that sweeps the rim’s open edge.

The temperature numbers, though, overlap more than people expect. Published operator guidance puts rim nights around 8 to 12 degrees Celsius and lake-area nights around 8 to 15 degrees, which means a calm rim night can feel milder than a damp, still lake night. What actually decides how cold your night feels is wind exposure on the pitch, condensation and dew in the morning, damp gear after a sweaty descent into the caldera, and whether mist rolls off the water after dark. The lake basin traps cold air and moisture in ways the raw elevation number does not predict.

Wind is the real differentiator. The rim camps sit on an exposed saddle where gusts can flatten a cheap tent and strip heat from anyone standing at the edge for sunset photos, while the lake shore, protected by the caldera walls, is far calmer. So if your priority is comfort, the honest ranking is: lake for calm and mild, rim for the view and the wind that comes with it.

Choose your camp nights for the itinerary, not for a thermometer. The lake night is there for the hot springs, the shoreline, and the morning climb out, and the rim night is there for the summit push and the caldera panorama, and swapping either one for a marginally warmer sleeping temperature is a bad trade. What you should demand from your operator instead is weather-worthy equipment: a sound tent pitched with its back to the wind, a dry sleeping bag rated for the conditions, and advice about that night’s actual pitch. We plan exactly that for every group, because on this mountain the right tent in the right spot matters more than 600 meters of elevation.