accumulated accumulations aged calcium-carbonate candle-shapes caves ceilings coloring colors colouring colours columns crystallisation crystallise crystallization crystallize deposits distinctive edge edges floors formation forms icicle-like minerals old Particles pillars pointed shape shaped shapes Singapore slow slow-growth slowly smooth Stalactite stalactites stalagmites subterranean surface surfaces texture textures unusual white above abstract aeroplane airplane appearance below between blue cloud cloud-formations clouds colored coloured conditions dark flight formations gray grey high in-between layers levels light multi-level patterns plane shadows skies sky sunlight travel up-above variations variety various various-cloud-formations weather weather-indicators