anhydrite buried cave dark geology grown gypsum light Mineral mountains natural old reflections rock rocks solid stone subterranean subterraneous tourist attraction water roof abstract accretions accumulations art artistic artwork bright color colorful coloring colors colour colourful colouring colours decorative distinctive down edge edges fantastic fantasy formations forms green lit multicolored multicoloured pointed red shape shaped shapes stalactites stalagmites surface surfaces suspended texture textures unusual UP yellow ceiling colored coloured creative curved curving decorated decoration decorations design designed detailed direction display eixt-tunnel exit floor flooring lighting lights mirrored mirrors passengers pedestrians people shiny Singapore subterranean-tunnel thoroughfare transportation-route Underground walled walls way-out accumulated aged calcium-carbonate candle-shapes caves ceilings columns crystallisation crystallise crystallization crystallize deposits floors formation icicle-like minerals Particles pillars slow slow-growth slowly smooth Stalactite white cavern caving compounds geological limestone mineral-deposits speleology speleothems spelunker spelunkering