Idar-Oberstein: Steinkaulenberg gemstone mine

Where: Continental · Europe · approx. 49.73, 7.3 (vicinity only)

Why this spot: Rockhounding locality: medieval agate and jasper mining district that built Germany's gem-cutting capital, Steinkaulenberg is the only gemstone mine in Europe open to visitors

What turns up: agate, jasper, rock crystal, amethyst druse fragments, smoky quartz

Access: Licensed / permit.

Fee visitor mine: underground tours ticketed, digging in the gem-bearing spoil is only via the mine's booked dig sessions, no freelance collecting in the protected mine area

Satellite view, historic-map overlays, tide/flow context and field notes are in the app. Exact research detail is part of Pro.