sand caves, sandhohlen in the harz mountains near blankenburg

harz national park cave caves sandhohlen sandhoehlen sandhöhlen sandstone sandsteinhohlen sansteinhoehlen regenstein fortress blankenburg sight attraction hiking trekking hike destination trail walk tour heers cultural landmark monument worship thingstead nature conservation protection area forest sand germany quartz rock rocks formation stone mystical mystic mysterious place location adventure nobody sandhutsche geology landscape mountains near