From the wiki source (https://content.time.com/time/subscriber/article/0,33009,967095,00.html https://content.time.com/time/subscriber/article/0,33009,967...)

From the wiki source (https://content.time.com/time/subscriber/article/0,33009,967095,00.html https://content.time.com/time/subscriber/article/0,33009,967...) > ...has been dividing his time between building the next generation of supercomputers and digging an underground tunnel that starts below his Chippewa Falls house and heads toward the nearby woods. "He's been working at it for some time now," says Rollwagen, who reports that the tunnel is 8 ft. high, 4 ft. wide and lined with 4-by-4 cedar boards. ... so at that point (1988), it was not yet finished