WALES - LLECHWED SLATE CAVERNS 1981 PHOTO POSTCARD  -  POSTAGE UNPAID BUT WITH A 5c LLECHWED UNDERGROUND RAILWAY SOUVENIR  LABEL,    TWO DIFF TYPES OF  CDS POSTMARKS,   ONE IS  "POSTED UNDERGROUND AT THE SLATE CAVERNS"    PICTURE SHOWS THE FLOODLIT UNDERGROUND LAKE.