The best-preserved of the Danish colonial sugar mill ruins on St. John, Annaberg sits on a hillside on the north shore with sweeping views over the sea towards the British Virgin Islands. Interpretive signs explain the workings of the plantation system — the mill, the windmill tower, the factory buildings — and address frankly the history of slavery that underpinned it all. The ruins are atmospheric and the views alone are worth the visit. Entry is free with a national park pass.