Clogwyn Coch Mine on Snowdon is perhaps the most "intersting" location in UK that comes to my mind; from the Llanberis path workings can be seen up a very steep set of cliff cum vertical scree. Only obvious access to higher workings would be to ab off the railway tracks (hope no train comes), or at this time of year from the bottom with ice gear. In prolonged cold weather big stopes become choked with spectacular ice formations.