The island of Timor has been rising due to tectonic shifts at almost the same rate as the rise in sea levels since the last age. This has exposed a great deal of quaternary limestone beds (ancient coral reefs) to the effects of tidal erosion. It has been confirmed that there are a number of fresh water filled cave sites located near and within Kupang, the principal city of West Timor and the provincial capital of East Nusa Tenggara. 2 of the main sites are: Gua Oehani (translated as Oehani Cave) and Gua Kristal (translated as Crystal Cave). While there is no requirement to hold a cave diving certificate to dive at either of these sites, competence equivalent to CDAA Advanced Cave and Cave/Advanced Cave appear to be the appropriate levels for these sites.