A modern regional museum in Bai Chay with exhibits covering the geology and ecology of Halong Bay, the history of the Quang Ninh province's coal industry, and local ethnography. The building itself is worth visiting — designed by a German architecture firm and genuinely striking by Vietnamese regional museum standards.
The geology section is the most rewarding: it explains how the limestone islands formed over 340 million years and provides context for what you see on the bay. The coal mining section is less prominent than the province's economic dependence on the industry would suggest, but gives useful background. Entry fee is modest; combined ticket available with the adjacent Quang Ninh Library.