The Shimane Museum of Ancient Izumo opened in 2007 adjacent to the shrine grounds and is arguably the best archaeological museum in the San'in region. It covers the prehistoric and early historic culture of the Izumo area, with particular depth on the Kofun period (3rd–7th centuries) during which the Izumo region was one of the most powerful in Japan. The collection includes hundreds of bronze bell-shaped ritual objects (dotaku) and iron swords found in local burial mounds — numbers that suggest the area was a major centre of early Japanese civilisation.
The museum's architecture by Kiyonori Kikutake is itself worth a look: a long, low building that echoes the horizontal lines of the shrine precincts, with a roof that cantilevers dramatically over the main entrance. English-language explanations are available throughout, which is not always the case at regional Japanese museums. Allow at least 90 minutes.