Rima Rau Burial Cave is a valuable piece of the region's heritage. Keep an eye out for any epitaphs which are often a bounty of illuminating facts.
You're spoiled for sightseeing choice when visiting Atiu. Rima Rau Burial Cave is a great place to kick off here, but there are numerous other interesting spots to consider. Cooks Landing, Anatakitaki Cave, and Oneroa Beach are close to the burial ground and and will cap off your day nicely.