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I am looking for a place to camp (tent, coming by bicycle or train), at walking distance from a beach, and not far from Tokyo.

Any recommendation?

I have found a few lists of camping addresses, but no reasonably exhaustive map.
There are lists in PDF format, but it is really hard to estimate location from that.
The ideal would be a Google-Maps-based mashup showing all campings, if that exists?

I am looking for a place to camp (tent, coming by bicycle or train), at walking distance from a beach, and not far from Tokyo.

Any recommendation?

I have found a few lists of camping addresses, but no reasonably exhaustive map.
There are lists in PDF format, but it is really hard to estimate location from that.
The ideal would be a Google-Maps-based mashup showing all campings, if that exists?