Aso is a small village in central 九州 Kyushu in 熊本県 Kumamoto Prefecture. In spite of being a small village, a lot of tourists stop here for a while. The reason is Aso's natural attraction 阿蘇山 Mount Aso.
Mount Aso is the largest still active volcano in Japan and among the largest in the world. This means you can stand on top of the huge crater and look right inside and see the water sulfur mix seething .
From Aso Station a bus will take you to the mountain for around 500 Yen. On the way I remember two stations: one was called Aso Youth Hostel and the other Aso Camping ground. So that are your options for sleeping here. Of course Aso being a little village in the midst of nature, you don't even need the camping ground, you can camp basically everywhere.
Like inactive 富士山 Mount Fuji, 阿蘇山 Mount Aso has been heavily developed for tourism. That means paved roads lead all the way up to the huge crater. You can go there even by car. Another option is a Cable Car that brings you from the bus station to the top for a horrendous sum. The best option is still walking. Walking from the Bus station to the top takes no more than 30 minutes and the road is not too steep.
Reaching the top you will find a catering station and a touristic area around the crater. At least they don't charge entrance... yet. That means depending on the season there will be many tourists looking down the crater, it can even get crowded when a whole tourist group arrives. However most don't stay very long and if you wait for a bit you should have most of the area for yourself (think in cable car arrival steps ;))
the station right next to the crater looks like a fortress
and indeed you can find little bunk shelters all around the crater area
there is also a temple for protecting the visitors
apparently Aso tourism has seen better times,
there were a couple of abandoned houses
What not many tourists notice is that the area around Mount Aso, which is not paved and secured by fences is also really wonderful and there are many more smaller craters to be found around. So if you have enough of Mass Tourism manufactured in Japan, you can sneak out of the road unseen and explore the area a bit. If you are a bit careful, I don't think its too dangerous, however there is one danger you should be aware of:
Mount Aso constantly spits out gigantic sulfur clouds out of the craters. The one from the huge crater are big and concentrated enough to kill humans by suffocation. That is why the tourist association has many helpers including a medical team there as well as a warning system. The system has basically four colors:
青 blue 0 ppm
currently no sulfur eruption
緑 green 0.2 - 2 ppm
minor sulfur eruption, people with Asthma, Bronchitis, breathing problems, heart problems and a weak stamina should be careful and take precautions
黄色 yellow 2 - 5 ppm
medium sulfur eruption people with Asthma, Bronchitis, breathing problems, heart problems and a weak stamina are forbidden to approach the crater, life threatening. Other people should be careful and take precautions.
赤 red more than 5 ppm
high sulfur eruption. Access forbidden to everyone, the air is not breathable.
At another spot precautions are described with medicine and brining a wet towel. If you breathe through the wet towel you can block most of the sulfur and suck the oxygen out of the air.
When I arrived we had yellow alert, for me having Asthma it would have meant it was too dangerous. However I am in excellent physical condition and my Asthma hasn't bothered me for quite some time, so I took the risk. I had my emergency spray at hand and prepared a wet towel, which I used for breathing and I was okay.
However if you to camp in the wilderness, take the sulfur into account. Spending there an hour is different from a whole night. The high sulfur percentage in the air will eventually get you, so be sure to get some distance between you and the craters.
Finally if you decide to spend a night here, you will have plenty of time left to walk around the wonderful nature here. There are several hiking trails you can follow, but when you feel adventurous, you can also get a whole area map at the station and just walk where you feel like. All area around the volcanoes is easily accessible and overgrown by an abundance of nature, due to the fertile volcanic ash ground. Be sure to take a compass with you and you should find your way through the green meadows and grey stone planes easily.
you can still see where the lava river was
So I found my way back to nature and found some time and tranquility to let the thoughts and impressions of the last days wander by. My next stop would be the number one destination for honey moons before flights to Hawaii became affordable...