A selection of photos from the UK's underground world.
ukThe Column in ShatterBaobab TreeRipply CurtainVastness of Cloud ChamberTop of Cloud ChamberElephant ChamberFlabergasam OxbowGaping GillHall of ColumnsJust the ColumnsIconic Trio of the Frozen DeepOctopusRippled RibbonSnake TeethSoda Straw ColumnsTall Drapery