The Chatham Islands Museum in Waitangi is the best first stop for understanding where you have landed. The islands' history is complicated and often painful, involving Moriori settlement, later Maori arrival, European sealing and farming, shipwrecks, and a long isolation from mainland New Zealand.
The museum is small, but on the Chathams small institutions carry a lot of weight. Exhibits and local knowledge help make sense of the landscapes you will see later: kopi groves, old mission sites, fishing settlements, and memorials that otherwise pass too quickly as roadside names.