Due to a slight case of temporal bungling on my part I had succeeded in missing the ideal train from Beppu to Aso the previous evening. So I was greatly relieved when I stumbled blearily from the train early the next morning to find James and the youth hostel owner waiting, van at the ready, to speed us on our way and allow us to catch the infrequent bus to the volcanoes.

In fact, we were already inside a crater. A giant rock wall encircles the horizon in the distance and the whole town of Aso lies inside this extinct monster. Towards the centre the rocks still hiss and bubble and, from time to time, baby volcanoes appear. The most active of these is, thankfully, only mildly restless. As we peered into its crater all we could see was a large steaming pool of churning milky blue water. A faintly sulphurous smell filled the air. The sides of the volcano were covered in a rich dark volcanic ash and, away from the tour groups, it was incredibly quiet: no birdsong, no running water, only the whisper of the wind. It is so barren and desolate. The next day we left the volcanoes and headed north, out of Kyushu towards our meeting with Gaynor in Hiroshima.

Miyajima is one of Japan's big tourist attractions. A picturesque island off the coast of Hiroshima, it is the home of the giant red Torii or Gate that stands in the sea and is featured in almost every brochure or article about Japan that has ever been published. Miyajima has a number of temples tucked away in the mountain-blanketing forest. They are very quiet too. The mixture of cool kanji-carved stone, moss, wood, and the occasional hint of colour provided by a small red bridge crossing a gurgling stream blend to produce an atmosphere of tranquillity and peace.

The peace in the Peace Park in the centre of Hiroshima was of an altogether different kind. We were there today. The first thing we came upon was the A-bomb dome - the former Industrial Promotions Centre preserved to serve as a reminder. It is a familiar icon, I have probably seen its picture a hundred times but, as in Nagasaki, standing in front of it made it unquestionably real. It wasn't a small ephemeral image on the page - it was a tall, solid, three-dimensional object. It stands, broken and crippled, a testament to an unimaginably terrible force.

As in Nagasaki the museum here is almost indescribable. Again, facts and figures numb and it is the images and objects that make the impact. Two models of Hiroshima sit side by side - separated by a few feet and a few minutes. One shows the city jammed with buildings, shops, streets, trees and parks. The next is a flat landscape - as if the hundreds of buildings and houses have simply dissolved. Charred rubble, blackened tree stumps and the odd shattered concrete or stone building are all that is left.

Remnants of this world sit behind glass panels: rubble melted into lava by the heat, bottles softened and bent and, more than anything, clothes - those worn by the parents and children who died then and in the aftermath. And then the awful pictures. And with them the realisation that these were only the pictures people could bear to take; many must have been too terrible to photograph. I came away drained.

But although the impact of the museum is incredible, it is not the most moving reminder in the park. That is, without a doubt, a small monument in the corner of the park - the monument to all the children who died. Curved around it, piled high, are hundreds of thousands of origami paper birds - cranes, standing as a symbol for peace and sent here by children the world over. Folded out of a hundred colours, it forms the park's only rainbow.