Possibly the only ‘desert’ in Japan is found on Mihara mountain on Oshima island, the biggest of the Tokyo Islands-group. Don’t think ‘sand dunes and camels’ or even rocks for that matter, this is volcanic territory and your hike here will be across ‘a plain of black.’ This vast lava field with occasional grassy bits and low scrubs makes for unearthly pictures especially when the clouds come in.
There is a hiking trail between the Oshima Onsen hotel and the summit of mount Mihara crossing this field. It is best to wear closed shoes because the loose lava can get ankle-deep in places and the small parts are very sharp! Views are great and the track easy to follow when the weather is clear. A great reward at the end is a soak in the baths of the Onsen hotel which is open to non-guests too.
To get a short visual impression, you can see this Youtube video by Tokaikisen