Sunriver sits on the ground of Camp Abbot, a World War II training camp for combat engineers that operated between 1943 and 1944. The camp was built rapidly in the ponderosa pine forest, trained tens of thousands of soldiers in bridge-building, demolition, and combat engineering, and was then largely torn down. The resort that replaced it in 1968 kept almost nothing from the military era.
The one exception is the Officers' Mess, a large log-and-timber building that now serves as the Great Hall, the main event and dining space of Sunriver Resort. You can walk through the lobby of the resort to see it — the building retains its original construction, and interpretive displays in the resort explain the camp's history. It is a modest piece of preservation, but given how thoroughly the rest of the site was cleared, the survival of this single building is notable.