Heyerdahl mentions that when the Europeans arrived in Polynesia, the people had "old pyramids, paved roads and carved stone statues as high as a four-storey house in Europe". Is there any truth to this, or was this an exaggeration of the Polynesian's engineering ability? Everyone knows of the Easter Island heads, but I was under the impression that those were very unique.
I'm not sure if this is the case for Polynesia, but I wouldn't be too surprised. There were certainly large developed communities in the Pacific, including in Polynesia. The most famous is in Micronesia, on the island of Pohnpei: Nan Madol which some people have called, "The Venice/Machu Pichu of the Pacfic". It is at the top of my bucket list of places to visit.
In terms of Polynesia, the closest I can think of are the burial tombs, or langi in Mu'a, the ancient capital of the Tu'i Tonga empire. They are certainly pretty impressive and suggestive of great development.
As an aside, the narrative in the west of Pacific Islanders as 'primitives' or 'savages', is totally unwarranted. Throughout Polynesia and Micronesia there existed highly developed socially stratified societies with complex agricultural techniques, material cultures and religions. Polynesian and Micronesian shipcraft was in many places better than that of the Europeans until well into the Renaissance and they had trading networks extending 1000s of kilometres.