World War II ended 64 years ago, but it comes to life every time Kenneth Rendell turns on the lights inside a squat, nondescript building in Natick. Amid the glitz of nearby shopping centers, the exterior is purposely plain to protect the anonymity of the place and its treasure - an evocative and jaw-dropping collection of more than 6,000 wartime artifacts Rendell has gathered over four decades.

For eight years, the Museum of World War II has been a preserve open only to a circle of Rendell acquaintances, historians, and military veterans or enthusiasts.

Within its walls, the museum houses a section of the sofa that Adolf Hitler and Eva Braun committed suicide on, silicon likenesses of the period's major figures outfitted in their actual uniforms, a Sherman tank, and a trove of historically significant letters and documents, including the complete plans for the invasion of Normandy and a draft of the 1938 Munich Agreement, with Hitler's handwritten changes.

No less an authority than Phil Reed, a former curator at Britain's Imperial War Museum, has said it "simply has no equal.''...