Sikidang Crater is Dieng at its most physical: sulphur steam, boiling mud, bare earth, and the sharp smell of volcanic gases. The main vent sits in open ground, so you can see the activity without a long climb.
It is also one of the plateau's busiest stops, with stalls and photo props around the entrance. Ignore those as best you can and focus on the crater itself. Stay on marked paths; this is unstable geothermal ground, not a theme park.