A beautiful lake on the top.
Mount Aso was actually much larger volcano which erupted and then collapsed many, many thousands of years ago. From that big crater, that is called caldera, a cone formed in the center with five peaks. One of them was very active during the past decades. I think I went to see Naka-dake, which is continuously emitting smoke and, as Wikipedia says, occasional eruptions. :D
I just made it barely in time to see the volcano from D section, which was not as close to the edge as B1 and B2 are, but it was still close enough! We could not breath properly, I was coughing all the time. And the smell..... oh that smell :)))
Wind was very strong and then all of a sudden it started to blow at our direction :))) And a minute later they evacuated us. It was interesting to watch people, mostly Korean tourists, quickening their pace down the hill :)
Mount Aso is a beautiful place, with splendid views from the top of the mountain. One could climb it also, there are roads for climbers. I'll do it maybe some other time. Though this time they didn't allow it because of some cow disease. Anyway Mount Aso should be one of the top destinations in Kyushu for every traveler. :))