Ruins Kalkoven Biebosch in Valkenburg aan de Geul

You're standing at the Biebosch lime kiln, also known as the Sibbergrubbe kiln, by the road from Sibbe to Valkenburg. Notice how the kiln is built right up against the hillside. That's no accident. Fuel and limestone went in at the top, and the burnt lime came out through the open front. Behind the kiln lies the Biebosch quarry, where limestone was dug out in the open air.