Even with hiking booths, you have to watch your step (surface is sandy slippery). For 1 mio IDR, you can get a palanquin and four carriers (probably only up to rim, not down to crater).
Interesting vegetation on crater rim:
You can walk around 3/4 of the crater rim, but at the dam it's impassable. Trek back to base camp:
sulfur mining site:
There was wild nasturtium, I tried some flowers and leaves, tastes like those in Germany (spicy similar to capers or papaya seeds).