In reply to Smythson:
Whether or not you need a map is beyond the point... some of us just like having maps. It isn't only about what is on the trail in front of you, it's about the area in general.
Marcel, if you haven't chosen a route already, I recommend taking the most common trail up, doing a lap of the crater, and taking the Gotemba trail down... it's a little bit more of a wrestle with public transport (which isn't usually a problem in the slightest in Japan) to get back to where you started, but you get to run down on huge fields of shifting black sand, making the descent quick, easy, and bloody good fun.
Post edited at 08:23