Goa Kristal — Crystal Cave — is a limestone cavern about 15 kilometres west of Kupang near the village of Bolok. The cave's main feature is a pool of remarkably clear freshwater at its base, lit from above by openings in the cave ceiling that turn the water a vivid blue-green. You swim in it rather than just look at it, which makes it one of the more memorable experiences near Kupang.
The descent into the cave requires climbing down a fixed ladder and some scrambling; it is not difficult but is not suitable for those with mobility issues. The water is cold. Entrance is cheap and there is usually a caretaker present. The cave is often listed under the name Goa Kristal Bolok to distinguish it from other cave sites in the area.