The cave was formed over thousands of years as rainwater slowly trickled through the limestone rock above. As it dripped, the water left tiny specks of the mineral calcite behind - and over a very long time those specks built up into the beautiful rock formations you see today.
Inside Harrison's Cave the temperature stays at about 26 °C all year round, so it feels pleasantly cool compared with the hot Caribbean sunshine outside. The rocks shimmer because crystals in the limestone catch the light, making the whole cave look a bit like the inside of a giant jewel.
Scientists have found that the cave system stretches for more than 2 kilometres beneath the island. Some chambers are tall enough to fit a three-storey building inside. The largest underground pool is nicknamed 'The Rotunda' and is a favourite spot for photographs.
Harrison's Cave opened to visitors in 1981 and is now one of the most popular attractions in all of the Caribbean. It shows just how much wonder can be hiding beneath your feet - even on a small island in the middle of the sea.