Antipodes Map – Antipodal location for any map point: I love this. It’s two Google Maps interfaces. Point the top one to your current location and the bottom one will reorient to your “antipodal” location, which is your exact opposite location. So, if you were to tunnel through the Earth from your current spot, your antipodal location is where you would pop out.
From Sioux Falls, I’d come up smack dab in the middle of the Indian Ocean.